Introduction to MicroProcessors and MicroControllers
1. INTRODUCTION 2 2. WHAT IS A MICROCOMPUTER? 3 2.1. WHAT IS A MICROPROCESSOR? 3 2.2. WHAT IS A MICROCONTROLLER? 4 2.3. WHAT IS AN EMBEDDED CONTROLLER? 5 3. THE MAJOR COMPONENTS OF A MICROCOMPUTER SYSTEM: 7 3.1. THE CPU 7 3.2. THE MEMORY 7 3.2.1. OPTIONS FOR STORING PROGRAMS. 8 3.3. THE I/O DEVICES 9 3.4. THE ADDRESS/DATA/CONTROL BUS (SYSTEM BUS) 12 4. A TYPICAL MICROPROCESSOR (Z80) 15 5. MICROCONTROLLER BASICS 17 5.0. A TYPICAL MIRCOCONTROLLER (I8051) 21 5.1. SOME OTHER POPULAR MICROCONTROLLERS 28 5.2. SPECIAL EASY CHIPS TO USE 31 5.3. INTEL 8052AH-BASIC 32 5.3.1. INSIDE THE 8052-BASIC 32 5.3.2. THE 8051 FAMILY 34 5.4. ELEMENTS OF THE 8052 AND 8052-BASIC 34 6. SPECIAL MICROCONTROLLER FEATURES 38 6.1. PERIPHERAL I/O 38 6.2. ADVANCED MEMORY OPTIONS 41 6.3. POWER MANAGEMENT AND LOW VOLTAGE 41 7. WRITING THE CONTROL PROGRAM 44 8. TESTING AND DEBUGGING 45 8.3. THE 8052-BASIC’S DEVELOPMENT SYSTEM 46
© by Heinz Rongen Forschungszentrum Jülich Zentrallabor für Elektronik 52425 Jülich, Germany email: [email protected]
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Heinz Rongen Forschungszentrum Jülich, ZEL 52425 Jülich, Germany Tel: +49-(0)2461-614512 Fax: +49-(0)2461-613990 Email: [email protected] 1. Introduction
Microprocessors or Microcontrollers are widely used, as controlling component in all kind of instruments. In this case the Microcontroller with its peripheral extensions is the major responsible component for the functionality of an instrument. If the controller fails, the complete instrument fails. Therefore this it very important to understand the major blocks inside of a microprocessor based system for maintenance and repair of such instruments. Such a controller system is call an embedded controller.
The microprocessor must often used for embedded controller systems are 8 bit µ- processors such as the 8080, 8085, Z80 or microcontrollers such as the 8751, 8052, 8032, 8048 etc. The older versions of controllers where mounted into a 40 pin DIP package, the modern are SMD components.
Surface Mounted Devices (SMD) and the Surface Mounting Technology (SMT) are the today’s technology for printed circuit boards in all application. With SMD devices all kind of instruments are getting smaller, cheaper and also more reliable. But for maintenance of these SMT boards the users needs much more sophisticated tools and experience to handle the SMD components without distroying the whole board.
This course demonstrates the building blocks and the repair of embedded control systems at two widely used standard processors. ¨ the TMPZ84c015 as an 8 bit microprocessor ¨ the 8052 as an 8 bit microcontroller All experiment boards are designed in SMD Technology for training soldering and unsoldering of SMD components.
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Heinz Rongen Forschungszentrum Jülich, ZEL 52425 Jülich, Germany Tel: +49-(0)2461-614512 Fax: +49-(0)2461-613990 Email: [email protected] 2. What is a Microcomputer?
A Microcomputer is a complete computer system comprising at least three major components, the microprocessor (CPU), Memory and IO peripheral components. A microcomputer could be a general purpose computer (like a PC) or a system designed to fulfill a special task. Memory I/O Eprom/Ram SIO/PIO (for example a controller system inside an instrument, microcontroller)
Address / Data / Control Bus
CPU
2.1. What is a Microprocessor? A Microprocessor is a device containing functions equivalent to a small computer’s Central Processing Unit (CPU). It is such capable of performing basic computer functions, an can be incorporated into system designs where such functions are required. A Microprocessor by definition means that this is only the central processing unit, with instruction decoder, registers and Arithmetic Logic processing Unit. Adress Bus A CPU does not include any memory or I/O components. ProgrammCounter
ALU Register
Instruction Decoder
Data Bus
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Heinz Rongen Forschungszentrum Jülich, ZEL 52425 Jülich, Germany Tel: +49-(0)2461-614512 Fax: +49-(0)2461-613990 Email: [email protected] 2.2. What is a Microcontroller? A Microcontroller is a Microcomputer in a single Chip. That means that a microcontroller chip includes a microprocessor (CPU) as well as some often used peripherals. A controller is used to control (makes sense!) some process or aspect of the environment. A typical microcontroller application is the monitoring of my house. As the temperature rises, the controller causes the windows to open. If the temperature goes above a certain threshold, the air conditioner is activated.
As the process of miniaturization continued, all of the components needed for a controller were built right onto one chip. A one chip computer, or microcontroller was born. A microcontroller is a highly integrated chip which includes, on one chip, all or most of the parts needed for a controller. The microcontroller could be called a "one-chip solution". It typically includes: · CPU (central processing unit or the microprocessor) · EPROM/PROM/ROM (Read Only Memory for the program code) · RAM (Random Access Memory for the data) · I/O (input/output) devices (serial, parallel, ADC, DAC etc.) · Timers · Interrupt controller
By only including the features specific to the task (control), cost is relatively low. A typical microcontroller has bit manipulation instructions, easy and direct access to I/O (input/output), and quick and efficient interrupt processing. Microcontrollers are a "one-chip solution" which drastically reduces parts count and design costs.
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Heinz Rongen Forschungszentrum Jülich, ZEL 52425 Jülich, Germany Tel: +49-(0)2461-614512 Fax: +49-(0)2461-613990 Email: [email protected] 2.3. What is an Embedded Controller? Simply (and naively stated) an embedded controller is a controller that is embedded in a greater system. You COULD say that an embedded controller is a controller (or computer) that is embedded into some device for some purpose other than to provide general purpose computing like a PC. In addition to control applications such as the above home monitoring system, microcontrollers are frequently found in embedded applications (embedded controllers?). Among the many uses that you can find one or more microcontrollers appliances (microwave oven, refrigerators, television and VCRs, stereos), automobiles (engine control, diagnostics, climate control), environmental control (greenhouse, factory, home), instrumentation, aerospace, and thousands of other uses.
A special application that microcontrollers are well suited for is data logging. Stick one of these chips out in the middle of a corn field or up in a balloon, and monitor and record environmental parameters (temperature, humidity, rain, etc.). Small size, low power consumption, and flexibility make these devices ideal for unattended data monitoring and recording.
Flavors Microcontrollers come in many flavors and varieties. Depending on the power and features that are needed, you might choose a 4 bit, 8 bit, 16 bit, or 32 bit microcontroller. In addition, some specialized versions are available which include features specific for communications, keyboard handling, signal processing, video processing, and other tasks. worldwide Microcontroller Shipments (in millions of dollars) '90 '91 '92 '93 '94 '95 '96 '97 4-bit 1,393 1,597 1,596 1,698 1,761 1,826 1,849 1,881 8-bit 2,077 2,615 2,862 3,703 4,689 5,634 6,553 7,529 16-bit 192 303 340 484 810 1,170 1,628 2,191 worldwide Microcontroller Shipments (in Millions) '90 '91 '92 '93 '94 '95 '96 '97 4-bit 778 906 979 1036 1063 1110 1100 1096 8-bit 588 753 843 1073 1449 1803 2123 2374 16-bit 22 38 45 59 106 157 227 313
Notice that even the lowly 4-bit device is holding its own - what use is a 16-bit part in a toaster oven? Also notice that the 8-bit market just keeps growing, and will probably continue to grow. 8-bit devices account for over half of the market, and will eventually grab even more. Now do you understand why every silicon manufacturer is really pushing their 8-bit microcontrollers?
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Heinz Rongen Forschungszentrum Jülich, ZEL 52425 Jülich, Germany Tel: +49-(0)2461-614512 Fax: +49-(0)2461-613990 Email: [email protected] Microcontroller (6)
Heinz Rongen Forschungszentrum Jülich, ZEL 52425 Jülich, Germany Tel: +49-(0)2461-614512 Fax: +49-(0)2461-613990 Email: [email protected] 3. The major components of a microcomputer system:
The major components of every computer are the CPU, Memory, I/O devices and the system bus. These components can be found in any computer system, anyway if it is a microprocessor or microcontroller based system.
3.1. The CPU CPU means Central Processing Unit. The CPU is the kernel of each computer. All datas (instructions and user data) is read from the CPU into the CPU registers. Instructions (the program code) are read into the instruction register, next they are decoded in the instruction decoder. Depending on the instruction as next following data fetches. The datas are stored in the arithemtic registers (accumulator), from there the are processed in te ALU (Arithmetic & Logic Unit). The ALU performs all arithmetical and logical processes on the data. The result from the ALU is written back into a CPU register. From there the data can be written back to the memory or an I/O device.
The most inportant signal from a CPU are the adress bus, data bus and control signals. These signals connecting the CPU to the memory and the I/O devices.
3.2. The Memory Every computer system needs a memory block. Memory can be external memory build by extra chips or the on chip memory of a microcontroller. In general there are two types of memory: · Program memory · Data memory Program memory is used to hold the application program. This must be memory which doesn’t loose his information at power down. At power up the CPU begins to read the instructions from this memory. In most microcomputer applications the program memory is a READ ONLY MEMORY (ROM). There are different types of ROM available. The most used is the EPROM. This chip could be programmed with a special programmer and could be erased by applying ultra-violet light. During the Microcontroller (7)
Heinz Rongen Forschungszentrum Jülich, ZEL 52425 Jülich, Germany Tel: +49-(0)2461-614512 Fax: +49-(0)2461-613990 Email: [email protected] normal use of this chip inside of the microcomputer system this memory can not be written, only read. Data memory is used for the dynamic data which is generated by the application program and for the STACK. The stack is a portion of memory where the CPU saves his own internal register data for calling a subroutine. Data memory must be able to read and write from the CPU, it is so called Random Access Memory (RAM). RAM chips looses the data when powered down.
The amount of memory in a microcomputer system depends strongly on the application. There are small controller applications which have only 512 Bytes ROM and 128 Bytes RAM. Bigger microcontroller application may have up to some Megabyte of EPROM and also RAM. Because of the 16 bit address bus of the most popular microcontrollers the address space is limited to 64 Kbyte. So you will find in many applications 32 Kbyte EROM and 32 Kbyte RAM.
3.2.1. Options for storing programs. Another consideration in circuit design is how to store programs. Instead of using disk storage, most microcontroller circuits store their programs on-chip. For one-of- kind projects or small-volume production, EPROM has long been the most popular method of program storage. Besides EPROMs, other options include EEPROM, ROM, nonvolatile (NV), or battery-backed, RAM, and Flash EPROM. The program memory may be in the microcontroller chip, or a separate component. To save a program in EPROM, you must set the EPROM’s data and address pins to the appropriate logic levels for each address and apply special programming voltages and control signals to store the data at the selected address. The programming process is sometimes called burning the EPROM. You erase the contents by exposing the chip’s quartz window, and the circuits beneath it, to ultraviolet energy. Some microcontrollers contain a one-time-programmable, or field-programmable, EPROM. This type has no window, so you can’t erase its contents, but because it’s cheaper than a windowed IC, it’s a good choice when a program is finished and the device is ready for quantity production. Several techniques are available for programming EPROMs and other memory chips. With a manual programmer, you flip switches to toggle each bit and program the EPROM byte by byte. This is acceptable for short programs, but quickly becomes tedious with a program of any length. Computer control simplifies the job greatly. With an EPROM programmer that connects to a personal computer, you can write a program at your keyboard, save it to disk if you wish, and store the program in EPROM in a few easy steps. Data Microcontroller (8)
Heinz Rongen Forschungszentrum Jülich, ZEL 52425 Jülich, Germany Tel: +49-(0)2461-614512 Fax: +49-(0)2461-613990 Email: [email protected] sheets for EPROMs rarely specify the number of erase and reprogramming cycles a device is guaranteed for, but a typical EPROM should endure 100 erase/program cycles, and usually many more.
EEPROMs are much like EPROMs except that they are electrically erasable—no ultraviolet source is required. Limitations of EEPROMs include slow speed, high cost, and a limited number of times that they can be reprogrammed (typically 10,000 to 100,000).
ROMs are cost-effective when you need thousands of copies of a single program. ROMs must be factory-programmed and once programmed, can’t be changed.
NVRAM typically includes a lithium cell, control circuits, and RAM encapsulated in a single IC package. When power is removed from the circuit, the lithium cell takes over and preserves the information in RAM, for 10 years or more. You can reprogram an NVRAM n infinite number of times, with the only limitation being battery life.
Flash EPROM is electrically erasable, like EEPROM, but most Flash devices erase all at once, or in a few large blocks, rather than byte-by-byte like EEPROM. Some Flash EPROMs require special programming voltages. As with EPROMs, the number of erase/program cycles is limited.
The 8052-BASIC uses two types of program memory. An 8-kilobyte, or 8K, on-chip ROM stores the BASIC-52 interpreter. For storing the BASIC-52 programs that you write, the BASIC-52 language has programming commands that enable you to save programs in external EPROM, EEPROM, or NVRAM.
Other memory. Most systems also require a way to store data for temporary use. Usually, this is RAM, whose contents you can change as often as you wish. Unlike EPROM, ROM, EEPROM, and NVRAM, the contents of the RAM disappear when you remove power the chip (unless it has battery back-up).
Most microcontrollers include some RAM, typically a few hundred bytes. The 8052- BASIC has 256 bytes of internal RAM. A complete 8052-BASIC system requires at least 1024 bytes of external RAM as well.
3.3. The I/O Devices In general a CPU with memory is ready to run. But of what need is a computer system without transaction to the real world? So every computer system needs some I/O devices. The word I/O-device is widespread. It could mean everything that is good for interfacing to the external world. Typical I/O devices are: ¨ keyboard controller for inputs from the user ¨ display controller for information to the user ¨ parallel I/O to switch on/off some lights or relays
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Heinz Rongen Forschungszentrum Jülich, ZEL 52425 Jülich, Germany Tel: +49-(0)2461-614512 Fax: +49-(0)2461-613990 Email: [email protected] ¨ serial I/O to communicate with other computers ¨ realtime clock so the computer knows the time and date ¨ analog inputs to measure a physical phenomena ¨ analog outputs to control a process
Finally, input/output (I/O) requires design decisions. Most systems require interfaces to things like sensors, keypads, switches, relays, and displays. Most microcontrollers have ports for interfacing to the world outside the chip. The 8052-BASIC uses many of its ports for accessing external memory and performing other special functions, but some port bits are available for user applications, and you can easily increase the available I/O by adding support chips.
Keyboards: A typical keyboard in embedded controller systems is build with 16 keys designes as a 4 by 4 matrix. The keyboard controller scans the X lines one by one at a time and looks for an response at the y lines. If a key is pressed then the keyboardcontroller knows from the X/Y information which key has been pressed and stores this information in an internal register. This information could be read from the CPU.
A commenly used keyboard controller is the 74 C 922 or 74 C 923. In some applikations there is no special keyboard controller. In this case the Keyboard controller scan of the keyboard matrix is done by the CPU itself trough a parallel I/O interface (PIO). to microprocessor
Displays: The Hardware needed for the display depends strongly on the used display. One often used display are the so callend 7-segment display. This are LED based display modules for displaying only numbers 0..9 and also the hex characters A..F. For driving the LEDs indise of these 7-segment display you need a component which delivers the needed current of about 10 mA per Segment. Also the decoding from the binary number (0..9 for example) to the segments which must be driven must be performed. The component 74 LS 47 is a typical binary to 7-segment display decoder.
Other Displays are the LCD Displays. Alpha-numeric modules display characters, numerals, symbols and some limited graphics. These LCD modules have their own controller. Interface is achieved via a bi-directional, parallel ASCII data bus. Microcontroller (10)
Heinz Rongen Forschungszentrum Jülich, ZEL 52425 Jülich, Germany Tel: +49-(0)2461-614512 Fax: +49-(0)2461-613990 Email: [email protected] Necessary features such as Character Generation, Display RAM Addressing, Cursor Scrolling, Blanking, and Handshake are all included. User programmable fonts are supported. In summary, these modules are the simplest and most economic means to communicate meaningfully between any micro-system and the outside world. Alpha-numeric modules range from 8 to 80 characters per line. One, two or four character lines may be chosen. Character height spans 0.130" (3.31 mm) to 0.500" (12.71 mm). Most formats are available in a variety of packages to meet various mounting requirements.
Parallel I/O: Parallel I/O is the most used I/O device in small microcomputer applications. A parallel I/O means that there are a number of static input or output bits. These outputs can be used to drive some lights, to switch some relays, to drive a display and so on. The input bits can be used to read information from switches etc. A simple parallel I/O can be done by a simple register component like a 74LS373. There are also some special parallel I/O components available, like the PIO 8255 or the Z80-PIO. With components the user can switch every bit as an input or output, so these component are very flexible for many application.
Serial I/O: Serial I/O is used to send data over longer distances to another computer system, display systems (terminal) or to a printer. While speaking about serial interfaces there are two words which describe the type of the serial interface: DTE is acronym for Data Terminal Equipment. Examples of DTE is computers, printers & terminals. DCE is acronym for Data Communication Equipment. Examples of DCE is modems. Wiring a cable for DTE to DCE communication is easy. All wires goes straight from pin x to pin x. But wiring a cable for DTE to DTE (nullmodem) or DCE to DCE requires that some wires are crossed. A signal should be wire from pin x to the opposite signal at the other end. With opposite signals I mean for example Transmit & Send.
Realtime clock: A realtimeclock is useful in application where the computer must known the absolute time and date, for example for switching on and off a peripheral device at a given day and time. Typical realtime clock component are the RTC62421 or RTC 72421 chip.
Analog inputs:
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Heinz Rongen Forschungszentrum Jülich, ZEL 52425 Jülich, Germany Tel: +49-(0)2461-614512 Fax: +49-(0)2461-613990 Email: [email protected] Many applications need a analog input for measuring a physical signal like a temperature or pressure. For measuring a physical phenomena you first need a sensor, which converts the physical phenomena into a electrical signal. Most of the sensors delivers a very small signal so at next you need some operational amplifiers to bring the signal into the level which is needed for the Analog to Digital Converter (ADC) (in most cases +/- 5 or +/- 10 Volt). The ADC itself is a single chip. There are many ADCs on the market. All of them have different speed and resolution. For microprocessor applications there are many ADCs with converting time of about 10 to 100 µs. For simple measurments there are ADCs with 8 bit resolution, mostly used today are the 12 bit resolution, but there are also ADCs with 16, 18, 20 and 22 bit resolution used in microprocessor systems.
Analog outputs: Analog outputs are used to control external devices by a linear voltage. This could be a High-Voltage supply where you can adjust the High-Voltage with an input voltage or another example could be a heater where you can adjust the heating power by a external voltage. Digital to Analog Converters (DAC) are used to generate a current or a voltage from the digital information written into a register. All the DACs need a operational amplifier behind their output pins to adjust their output level to the voltage needed for the external device. Also here are a lot of DAC on the market, with bit resolutions ranging from 8, 12, up to 16 bit.
Because of the big ADC and DAC component market it is very difficult to give here some component examples. Insteed I will say that there are some big component companies which are great on the analog IO market. If you see a component with a Label of: Analog Devices Burr Brown Maxim ... then in most cases these are components for the analog I/O section.
3.4. The Address/Data/Control Bus (system bus)
The system bus (address/data/control lines) is the connection between the several components of a microprocessor system. The data bus with depends on the microprocessor (8, 16 or 32 bits), the address bus is at least 16 bit wide. The system bus is used for every datatransfer between the Memory and the CPU for operationcode fetches, for datatransfer to and from the RAM for dynamic data fetch and also for data to and from the I/O devices. The transaction over the system bus can be grouped into two groups: · a read cycle: data from the Memory or I/O device into the CPU · a write cycle: data from the CPU to the Memory or I/O device
The control lines of the system bus controls what kind of data transfer is in process. Microcontroller (12)
Heinz Rongen Forschungszentrum Jülich, ZEL 52425 Jülich, Germany Tel: +49-(0)2461-614512 Fax: +49-(0)2461-613990 Email: [email protected] The most important control lines are: · the CHIPSELECT signal *CS · the READ signal *RD · the WRITE signal *WR (asterix means that this signal is low aktiv)
Every bustransfer is started with the output of an address onto the address lines. The lower address line are direct connected to the Memory. Some address line (the upper lines) are used for address decoding. Adress decoding means that there is a logic circuits which decides based on the address what device (EPROM, RAM I/O device) should be activated. The address decoder then gives a unique CHIP SELECT (CS) signal to that device. For that, every device in a microprocessorsystem needs a unique address.
The CS signal tells the device that it should transmit data in this bus cycle. At next one of the signals RD or WR is activated from the CPU. This tells the device if it should send data to the CPU (Read cycle) or receive data from the CPU (Write cycle).
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Heinz Rongen Forschungszentrum Jülich, ZEL 52425 Jülich, Germany Tel: +49-(0)2461-614512 Fax: +49-(0)2461-613990 Email: [email protected] General Bustiming diagram:
valid address valid address from the CPU from the CPU
Chip select to a Chip select to a device device Chip Select: *CS
Read signal: *RD a READ cycle a WRITE cycle Write signal: *WR
Data lines: D0..D7
valid data from valid data from Access time the deviceto the the CPU to the CPU device
Every bus cycle (Reads and Writes) starts with a valid address from the CPU. As next the address decoder generates a unique CHIP SELECT for one device. Then the RD or WR signal is activated from the CPU to tell wether it is a read or write operation. By a read operation the device has to drive the data to the data bus, this could take a short time (data access time), but the datas must be stable at the rising edge of the RD signal. With the rising edge of the RD signal the CPU latches the data internal. In a write cycle the CPU itselfs drive the data bus. Also in this case it is not sure that the data is stable at the beginning of the cycle. The data must be stable at the rising edge of the WR cycle, so that the device could also latch the data with the rising edge of the WR signal.
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Heinz Rongen Forschungszentrum Jülich, ZEL 52425 Jülich, Germany Tel: +49-(0)2461-614512 Fax: +49-(0)2461-613990 Email: [email protected] 4. A typical microProcessor (Z80)
I get really nervous reading the trade press. Magazines will have you believe that the only viable processor for even the simplest applications is a 50 Mhz 486 or a screaming RISC machine. How many designers are using these CPUs in their embedded designs? Personally, I prefer 8 and 16 bit CPUs. They're cheap, they're cheap to interface to, and they are easy to work with. Remember that 16 and 32 bit machines will have 2 or 4 ROM and RAM chips per word, compared to 1 for an 8 bit processor, greatly increasing memory costs. In fact, an 8 bit processor exactly matches the bus width of the vast majority of memories and peripherals. An 8 bit bus uses memory efficiently. Simpler circuitry, with fewer components, can be used.
I feel four processor families can satisfy most embedded designs. I'll leave out 4 bit choices, as these applications are often so specialized that a custom or semi-custom chip is often the most cost effective solution. My choices are the 8051 family, the Z80 family, the 80186 (and V-Series) families, and the 68000 and its derivatives. In this document I will do my explanations about microprocessor on the example of the Z80 and his derivates.
Current Z80 Technology
The Z80 is essentially unchanged from the original version introduced in the mid- 70s. Now CMOS versions are common, and clock rates have skyrocketed. Zilog's newest offering runs at 20 Mhz. This speed is no panacea- it comes at the price of expensive ROMs and RAMs. Still, even at 6 to 10 Mhz the Z80 has respectable performance. It would be a terrible Windows machine, but is more than adequate for an awful lot of embedded systems.
The Z80 itself is attractive due to its low cost and wide availability. It's pretty easy to find Z80s for less than a buck. Tools are everywhere. Though its index instructions are a little crude, it is a far better C machine than, say, the 8051. The Z80 in isolation would be a dead-end line. What makes it interesting is the high integration derivatives CPUs spawned by the architecture. All four of the processor families I mentioned earlier exist in multiple proliferation versions. A processor by itself is useful; one integrated with a number of on-chip peripherals is compelling.
The 64180 is a Hitachi-supplied Z80 core with numerous on-chip "extras". Zilog's version is the Z180, which is essentially the same part. As of this writing, Zilog sells parts running at speeds to 15 Mhz. The 64180/Z180 microprocessor integrates many of the functions traditionally assigned to peripheral circuitry onto a single chip. The designers picked an architecture compatible with the Z80, giving Z80 users a completely software compatible upgrade path. Old Z80 designs can be converted to the 64180 with essentially no loss in software investment. New designs will benefit from the processor's low cost, powerful instruction set, minute power consumption, and high level of integration. Microcontroller (15)
Heinz Rongen Forschungszentrum Jülich, ZEL 52425 Jülich, Germany Tel: +49-(0)2461-614512 Fax: +49-(0)2461-613990 Email: [email protected] Both Toshiba and Zilog sell the 84013 and 84015, which are Z80 cores with conventional Z80 peripherals integrated on-board. These processors are natural migration paths for current users of Z80s wishing to reduce systems costs. Both the 84013 and the 84015 include one SIO (Z80-specific Serial I/O), and one CTC (again, a Z80-specific timer part). The SIO and CTC are functionally identical to the discrete chip SIO/CTC used in so many older designs. In addition, the newer parts include a watchdog timer and clock generator. The 84015 comes in a 100 pin quad flat pack. To take advantage of the extra pins the vendors added in a Z80-like PIO (parallel I/O) port, with 16 parallel lines and 4 handshaking likes.
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Heinz Rongen Forschungszentrum Jülich, ZEL 52425 Jülich, Germany Tel: +49-(0)2461-614512 Fax: +49-(0)2461-613990 Email: [email protected] 5. Microcontroller Basics This chapter introduces you to the world of microcontrollers, including definitions, some history, and a summary of what’s involved in designing and building a microcontroller project. A microcontroller is a computer-on-a-chip, or, if you prefer, a single-chip computer. Micro suggests that the device is small, and controller tells you that the device might be used to control objects, processes, or events. Another term to describe a microcontroller is embedded controller, because the microcontroller and its support circuits are often built into, or embedded in, the devices they control. You can find microcontrollers in all kinds of things these days. Any device that measures, stores, controls, calculates, or displays information is a candidate for putting a microcontroller inside. The largest single use for microcontrollers is in automobiles ,just about every car manufactured today includes at least one microcontroller for engine control, and often more to control additional systems in the car. In desktop computers, you can find microcontrollers inside keyboards, modems, printers, and other peripherals. In test equipment, microcontrollers make it easy to add features such as the ability to store measurements, to create and store user routines, and to display messages and waveforms. Consumer products that use microcontrollers include cameras, video recorders, compact-disk players, and ovens. And these are just a few examples. A microcontroller is similar to the microprocessor inside a personal computer. Examples of microprocessors include Intel’s 8086, Motorola’s 68000, and Zilog’s Z80. Both microprocessors and microcontrollers contain a central processing unit, or CPU. The CPU executes instructions that perform the basic logic, math, and data- moving functions of a computer. To make a complete computer, a microprocessor requires memory for storing data and programs, and input/output (I/O) interfaces for connecting external devices like keyboards and displays. In contrast, a microcontroller is a single-chip computer because it contains memory and I/O interfaces in addition to the CPU. Because the amount of memory and interfaces that can fit on a single chip is limited, microcontrollers tend to be used in smaller systems that require little more than the microcontroller and a few support components. Examples of popular microcontrollers are Intel’s 8052 (including the 8052-BASIC, which is the focus of this book), Motorola’s 68HC11, and Zilog’s Z8.
A Little History To understand how microcontrollers fit into the always-expanding world of computers, we need to look back to the roots of microcomputing. In its January 1975 issue, Popular Electronics magazine featured an article describing the Altair 8800 computer, which was the first microcomputer that hobbyists could build and program themselves. The basic Altair included no keyboard, video display, disk drives, or other elements we now think of as essential elements of a personal computer. Its 8080 microprocessor was programmed by flipping toggle switches on the front panel. Standard RAM was 256 bytes and a kit version cost $397 ($498 assembled). A breakthrough in the Altair’s usability occurred when a small company called Microsoft offered a version of the BASIC programming language for it. Microcontroller (17)
Heinz Rongen Forschungszentrum Jülich, ZEL 52425 Jülich, Germany Tel: +49-(0)2461-614512 Fax: +49-(0)2461-613990 Email: [email protected] Of course, the computer world has changed a lot since the introduction of the Altair. Microsoft has become an enormous software publisher, and a typical personal computer now includes a keyboard, video display, disk drives, and Megabytes of RAM. What’s more, there’s no longer any need to build a personal computer from scratch, since mass production has drastically lowered the price of assembled systems. At most, building a personal computer now involves only installing assembled boards and other major components in an enclosure. A personal computer like Apple’s Macintosh or IBM’s PC is a general-purpose machine, since you can use it for many applications—word processing, spreadsheets, computer-aided design, and more—just by loading the appropriate software from disk into memory. Interfaces to personal computers are for the most part standard ones like those to video displays, keyboards, and printers.
But along with cheap, powerful, and versatile personal computers has developed a new interest in small, customized computers for specific uses. Each of these small computers is dedicated to one task, or a set of closely related tasks. Adding computer power to a device can enable it to do more, or do it faster, better, or more cheaply. For example, automobile engine controllers have helped to reduce harmful exhaust emissions. And microcontrollers inside computer modems have made it easy to add features and abilities beyond the basic computer-to-phone-line interface. In addition to their use in mass-produced products like these, it’s also become feasible to design computer power into one-of-a-kind projects, such as an environmental controller for a scientific study or an intelligent test fixture that ensures that a product meets its specifications before it’s shipped to a customer. At the core of many of these specialized computers is a microcontroller. The computer’s program is typically stored permanently in semiconductor memory such as ROM or EPROM. The interfaces between the microcontroller and the outside world vary with the application, and may include a small display, a keypad or switches, sensors, relays, motors, and so on. These small, special-purpose computers are sometimes called single-board computers, or SBCs. The term can be misleading, however, since the computer doesn’t have to be on a single circuit board, and many types of computer systems, such as laptop and notebook computers, are now manufactured on a single board.
New Tools To design and build a computer-controlled device, you need skills in both circuit design and software programming. The good news is that a couple of recent advances have simplified the tasks involved. One is the introduction of microcontrollers themselves, since they contain all of the elements of a computer on a single chip. Using a microcontroller can reduce the number of components and thus the amount of design work and wiring required for a project. The 8052-BASIC microcontroller even includes its own programming language, called BASIC-52. The other development is personal computers themselves. A desktop computer can help tremendously by serving as a host system for writing and testing programs. As you are developing a project, you can use a Microcontroller (18)
Heinz Rongen Forschungszentrum Jülich, ZEL 52425 Jülich, Germany Tel: +49-(0)2461-614512 Fax: +49-(0)2461-613990 Email: [email protected] serial link to connect the host system to a target system, which contains the microcontroller circuits you are testing. You can then use the personal computer’s keyboard, video display, disk drives, and other resources for writing and testing programs and transferring files between the two systems.
The 8052-BASIC chip described in this book is perfect for many simpler applications, especially control and monitoring tasks. Because the chip is easy to use, it’s a good way to learn about microcontrollers and computers in general. Although you can’t do the most complex projects with it, you can do a lot, at low cost and without a lot of hassle.
Choosing a chip. Does it matter which microcontroller chip you use? All microcontrollers contain a CPU, and chances are that you can use any of several devices for a specific project. Within each device family, you’ll usually find a selection of family members, each with different combinations of options. For example, the 8052-BASIC is a member of the 8051 family of microcontrollers, which includes chips with program memory in ROM or EPROM, and with varying amounts of RAM and other features. You select the version that best suits your system’s requirements.
Microcontrollers are also characterized by how many bits of data they process at once, with a higher number of bits generally indicating a faster or more powerful chip. Eight-bit chips are popular for simpler designs, but 4-bit, 16-bit, and 32-bit architectures are also available. The 8052-BASIC is an 8-bit chip. Power consumption is another consideration, especially for battery-powered systems. Chips manufactured with CMOS processes usually have lower power consumption than those manufactured with NMOS processes. Many CMOS devices have special standby or “sleep” modes that limit current consumption to as low as a few microamperes when the circuits are inactive. Using these modes, a data logger can reduce its power consumption between samples, and power up only when it’s time to take data. The 8052-BASIC chip is available in both NMOS and CMOS versions. The original 8052-BASIC was an NMOS chip, offered directly from Intel. (Intel’s term for its NMOS process is HMOS.) Although Intel never offered a CMOS version directly, Micromint became a source by ordering a batch of CMOS 8052’s with the BASIC-52 programming language in ROM. The CMOS version, the 80C52-BASIC, has maximum power consumption of 30 milliamperes, compared to 175 milliamperes for the NMOS 8052-BASIC. All microcontrollers have a defined instruction set, which consists of the binary words that cause the CPU to carry out specific operations. For example, the instruction 0010 0110 tells an 8052 to add the values in two locations. The binary instructions are also known as operation codes, or opcodes for short. The opcodes perform basic functions like adding, subtracting, logic operations, moving and copying data, and controlling program branching. Control circuits often require reading or changing single bits of input or output, rather than reading and writing a byte at a time. For example, a microcontroller might use the eight bits of an output port to switch power to eight sockets. If each socket must operate independently of the others, a way is needed to change each bit without affecting the
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Heinz Rongen Forschungszentrum Jülich, ZEL 52425 Jülich, Germany Tel: +49-(0)2461-614512 Fax: +49-(0)2461-613990 Email: [email protected] others. Many microcontrollers include bit-manipulation (also called Boolean) opcodes that easily allow programs to set, clear, compare, copy, or perform other logic operations on single bits of data, rather than a byte at a time.
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Heinz Rongen Forschungszentrum Jülich, ZEL 52425 Jülich, Germany Tel: +49-(0)2461-614512 Fax: +49-(0)2461-613990 Email: [email protected] 5.0. A typical mircoController (i8051)
The 8051 is an 8 bit microcontroller originally developed by Intel in 1980. It is the world's most popular microcontroller core, made by many independent manufacturers (truly multi-sourced). There were 126 million 8051s (and variants) shipped in 1993!!
A typical 8051 contains: Þ CPU with Boolean processor Þ 5 or 6 interrupts: 2 are external, 2 priority levels Þ 2 or 3 16-bit timer/counters Þ programmable full-duplex serial port (baud rate provided by one of the timers) Þ 32 I/O lines (four 8-bit ports) Þ RAM Þ ROM/EPROM in some models
Blockdiagram of the 8052 microcontroller:
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Heinz Rongen Forschungszentrum Jülich, ZEL 52425 Jülich, Germany Tel: +49-(0)2461-614512 Fax: +49-(0)2461-613990 Email: [email protected] The 8051 architecture is a tad bizarre, but then so are the architectures of most microcontrollers due to their specialization (check out the PIC for creativity). One vexing problem with the 8051 is its very non-orthogonal instruction set - especially the restrictions on accessing the different address spaces. However, after some time programming the chip, you can get used to it - maybe even appreciate it. One strong point of the 8051 is the way it handles interrupts. Vectoring to fixed 8- byte areas is convenient and efficient. Most interrupt routines are very short (or at least they should be), and generally can fit into the 8-byte area. Of course if your interrupt routine is longer, you can still jump to the appropriate routine from within the 8 byte interrupt region.
The 8051 instruction set is optimized for the one-bit operations so often desired in real-world, real-time control applications. The Boolean processor provides direct support for bit manipulation. This leads to more efficient programs that need to deal with binary input and output conditions inherent in digital-control problems. Bit addressing can be used for test pin monitoring or program control flags.
8051 Flavors The 8051 has the widest range of variants of any embedded controller on the market. The smallest device is the Atmel 89c1051, a 20 Pin FLASH variant with 2 timers, UART, 20mA. The fastest parts are from Dallas, with performance close to 10 MIPS! The most powerful chip is the Siemens 80C517A, with 32 Bit ALU, 2 UARTS, 2K RAM, PLCC84 package, 8 x 16 Bit PWMs, and other features.
Among the major manufacturers are: AMD Enhanced 8051 parts (no longer producing 80x51 parts) Atmel FLASH and semi-custom parts Dallas Battery backed, program download, and fastest variants Intel 8051 through 80c51gb / 80c51sl Matra 80c154, low voltage static variants OKI 80c154, mask parts Philips 87c748 through 89c588 - more variants than anyone else Siemens 80c501 through 80c517a, and SIECO cores SMC COM20051 with ARCNET token bus network engine SSI 80x52, 2 x HDLC variant for MODEM use
8051 representatives and approximate prices (in USD $) There are many, many varieties of 8051 out there. This is only a small sampling of typical prices on Intel chips. 8031 (128 bytes RAM) 3.59 80C31 (CMOS version of previous) 6.95 8051AH (256 bytes RAM) 6.95 8052AHBASIC (w/Basic interpreter built in) 29.95 8751 (4K EPROM, 128 bytes RAM) 26.95 87C51 (CMOS version of previous) 39.95 Microcontroller (22)
Heinz Rongen Forschungszentrum Jülich, ZEL 52425 Jülich, Germany Tel: +49-(0)2461-614512 Fax: +49-(0)2461-613990 Email: [email protected] 89C2051 (ATMEL 2K FLASH, 128 bytes RAM, 20-pin) 3.30
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Heinz Rongen Forschungszentrum Jülich, ZEL 52425 Jülich, Germany Tel: +49-(0)2461-614512 Fax: +49-(0)2461-613990 Email: [email protected] 8051 Types of Memory Before we delve into the guts of the 8051, it is important to define the four types of memory that are available. The distinction between each type of memory is important because different assembly language instructions are used to access each type of memory, and each type of memory has unique qualities which must be considered when first designing the hardware and/or software.
The four types of memory are: Internal RAM. The microcontroller contains a small amount of on-chip RAM which is used primarily for internal program registers, the stack, and often user variables which need to be accessed quickly or on a frequent basis. In the 8051 and 8031 models, the total amount of Internal RAM is 128 bytes. In the 8052 and 8032 models, the total amount of Internal RAM is 256 bytes (an easy way to remember this is by looking at the last digit of the model of the chip: a "1" means 128 bytes, and a "2" means 256 bytes). It is important to remember that the internal "R" registers, the stack, and the "bit registers" (more on all these later) all share these precious 128 or 256 bytes of Internal RAM. Thus it is often important to use space within Internal RAM for variable storage on a very sparing basis to avoid problems, particularly stack overflows. The Internal RAM is volatile (it's contents are lost when the power fails) and is the fastest type of memory available in an 8051 architecture since it is "on-chip."
External RAM. The microcontrollers ability to accept external RAM allows you to handle greater quantities of data than would otherwise be possible if you were restricted to the 8051's Internal RAM. As the name suggests, External RAM is additional Random-Access-Memory which is external to the chip itself. External RAM, like Internal RAM, is volatile so it's contents will be lost when the power fails. Like EPROM memory, External RAM is limited to 64k (Note: you may have 64k of RAM and 64k of EPROM at the same time). External RAM is not as fast as Internal RAM since the microcontroller has to move the bytes to/from the External RAM chip(s). Like External EPROM memory, the use of External RAM will cause you to lose 16 of the 32 input/output lines normally available. Note: If you use both External EPROM and External RAM, you will lose the same 16 input/output line. That is to say, you don't lose 16 bits for each type of External memory used, just for the fact that some type of external memory is used.
Internal EPROM. Several models of the 8051 microcontroller (specifically, the 8751 and the 8752) offer an on-chip EPROM. This means rather than using an external EPROM chip, you may burn your program directly into the 8751 (or 8752). This has a number of important advantages: · Since your program is stored on-chip, an additional EPROM chip (and circuit design to support it) is unnecessary. · When your program is stored on-chip you do not lose the 16 input/output lines that you lose when using an External EPROM. · The chip can be configured to prevent the contents of the EPROM from being read off the chip.
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Heinz Rongen Forschungszentrum Jülich, ZEL 52425 Jülich, Germany Tel: +49-(0)2461-614512 Fax: +49-(0)2461-613990 Email: [email protected] A disadvantage of external EPROM’s is that anyone can read the contents and reverse engineer your code. Using Internal EPROM, you can burn your program onto the 8751/8752 and instruct it to deny read access by would-be hackers. The drawbacks to Internal EPROM’s is that the chips themselves are somewhat more expensive and that the amount of EPROM space is limited to 4k (8751) or 8k (8752) which may make it a non-option if your program is large.
External EPROM. The microcontroller is generally pretty useless unless you can somehow run your "program" on it. One of the most common ways of running your program is to compile it and subsequently "burn" it into a separate EPROM chip. The 8051 can then be attached to the EPROM at the hardware level such that the microcontroller will run the program stored in the EPROM. Since your code is "burned" into the EPROM, the contents are not lost when the power fails. However, since it is a type of "ROM" (Read Only Memory) it is not possible for your program to modify the data stored therein. Thus, it is ideal for storing your program and other constants. The 8051 can access up to 64k (65536 bytes) of EPROM memory. Your programs, thus, are limited to 64k (there are actually tricks involving specialized circuit design and specialized support software that can break the 64k program limit, but without taking these fancy steps the limit is 64k). Additionally, if an External EPROM is used you will lose 16 of the 32 input/output lines normally available to you.
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Heinz Rongen Forschungszentrum Jülich, ZEL 52425 Jülich, Germany Tel: +49-(0)2461-614512 Fax: +49-(0)2461-613990 Email: [email protected] 8051 Memory Access Procedure When using externel memory with the 8052 then port 0 and port 1 are used as a multiplexed address/data bus. By this you loose 16 of the 32 I/O bits, but for this you can extend your external address range to 64 Kbyte external locations. (EPROM, RAM or also memory mapped I/O devices) A multiplexed address/data bus means that the lower lines of this 16 bit interface is used as an part of the adress and later as datalines. The access to external memory is as followed. Whenever the 8051 requires access (either read or write) to External Data Memory (RAM), the following sequence of events takes place:
· The full address is loaded into pins Addr0 through Addr15. · The ALE pin is strobed for a short period of time. · The lower byte of the address (Addr0 through Addr7) is replaced by the bits of the data to be written. · After a short delay, either the WR, RD or PSEN pin is strobed to execute the memory access operation. WR and RD deal with access to external data memory (RAM) whereas PSEN deals with access to external code memory (such as from an EPROM).
The logic behind this is that by doubling the function of pins port0-0 through port0-7 more effective use of pins is achieved. That is to say, if these pins did not serve double-functions the 8051 would either require an additional 8 pins (48 pins instead of 40) or would cause an additional 8-bit port to become unavailable when external memory was used. Since neither of these are desirable options, the designers of the 8051 chose to use pins port0-0 through port0-7both to transmit the low-byte of the address and to also transmit the data itself. As you can see by reviewing the four step procedure above, the ALE pin is strobed when pins port0-0 through port0-7 contain the low-byte of the address. When ALE is
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Heinz Rongen Forschungszentrum Jülich, ZEL 52425 Jülich, Germany Tel: +49-(0)2461-614512 Fax: +49-(0)2461-613990 Email: [email protected] strobed, therefore, we need to store and hold the value of the low-byte of memory so that those 8 bits are still available when the actual read or write operation takes place (when RD or WR is strobed). This is easily accomplished using a simple Octal Latch, such as the 74HCT373.
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Heinz Rongen Forschungszentrum Jülich, ZEL 52425 Jülich, Germany Tel: +49-(0)2461-614512 Fax: +49-(0)2461-613990 Email: [email protected] 5.1. Some other popular microcontrollers Some common microcontrollers are described below. A common question is "what microcontroller should I use for...?" Well, that's a tough one. The best advice would be to choose a chip that has a full set of development tools at the price you can afford, and good documentation. For the hobbyist, the Intel 8051, Motorola 68hc11, or Microchip PIC would all make suitable choices.
8048 (Intel) The granddaddy of 'em all, the first microcontroller, it all started here! Although a bit long in the tooth and a bit kludgey in design (at least by today's standards), it is still very popular due to its very low cost, availability, and wide range of development tools. Modified Harvard architecture with program ROM on chip with an additional 64 to 256 bytes of RAM also on chip. I/O is mapped in its own space.
8051 (Intel and others) The 8051, Intel's second generation of microcontrollers, rules the microcontroller market at the present time. Although featuring a somewhat bizarre design, it is a very powerful and easy to program chip (once you get used to it). Modified Harvard architecture with separate address spaces for program memory and data memory. The program memory can be up to 64K. The lower portion (4K or 8K depending on type) may reside on chip. The 8051 can address up to 64K of external data memory, and is accessed only by indirect addressing. The 8051 has 128 bytes (256 bytes for the 8052) of on-chip RAM, plus a number of special function registers (SFRs). I/O is mapped in its own space. The 8051 features the so-called "Boolean processor". This refers to the way instructions can single out bits just about anywhere (RAM, accumulators, I/O registers, etc.), perform complex bit tests and comparisons, and then execute relative jumps based on the results. Piles of software, both commercial and free, are available for the 8051 line. Many manufacturers supply what must be a hundred different variants of this chip for any requirement.
80c196 (MCS-96) The third generation of Intel microprocessors, the 80c196 is a 16 bit processor. Originally fabricated in NMOS (8096), it is now mainly available in CMOS. Among the many features it includes are: hardware multiply and divide, 6 addressing modes, high speed I/O, A/D, serial communications channel, up to 40 I/O ports, 8 source priority interrupt controller, PWM generator, and watchdog timer.
80186,80188 (Intel) These chips are, in essence, microcontroller versions of the 8086 and 8088 (of IBM/PC fame). Included on the chip are: 2 channels of DMA, 2 counter/timers, programmable interrupt controller, and dynamic RAM refresh. There are several variations including: low power versions, variations with serial ports, and so on.
80386 EX (Intel)
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Heinz Rongen Forschungszentrum Jülich, ZEL 52425 Jülich, Germany Tel: +49-(0)2461-614512 Fax: +49-(0)2461-613990 Email: [email protected] The 80386 EX is of course a 386 in microcontroller clothing. Included on the chip are: serial I/O, power management, DMA, counter/timers, programmable interrupt controller, and dynamic RAM refresh. And of course, all of the power of the 386 microprocessor.
TMS370 (Texas Instruments) It is similar to the 8051 in having 256 registers, A and B accumulators, stack in the register page, etc. It also has a host of onboard support devices, some members have all of them while others have a subset, the peripherals include: RAM, ROM (mask, OTP, or EEPROM), 2 timers (configurable as timers/ counters/ comparators/ PWM output), watchdog timer, SCI (synchronous serial port), SPI (asynchronous serial port), A/D (8 bit, 8 channel), interrupts.
6805 (Motorola) The 6805 is based loosely on the manufacturer's earlier 6800, with some similarities to the 6502. It has a Von-Neuman architecture in which instructions, data, I/O, and timers all share the same space. Stack pointer is 5 bits wide which limits the stack to 32 bytes deep. Some members of this family include on chip A/D, PLL frequency synthesizer, serial I/O, and software security.
68hc11 (Motorola and others) The popular 68hc11 is a powerful 8-bit data, 16-bit address microcontroller from Motorola (the sole supplier) with an instruction set that is similar to the older 68xx parts (6801, 6805, 6809). The 68hc11 has a common memory architecture in which instructions, data, I/O, and timers all share the same memory space. Depending on the variety, the 68hc11 has built-in EEPROM/OTPROM, RAM, digital I/O, timers, A/D converter, PWM generator, pulse accumulator, and synchronous and asynchronous communications channels. Typical current draw is less than 20ma.
PIC (MicroChip) The PIC microcontrollers were the first RISC microcontrollers. RISC generally implies that simplicity of design allows more features to be added at lower cost, and the PIC line is no exception. Although having few instructions (eg. 33 instructions for the 16C5X line versus over 90 for the Intel 8048), the PIC line has a wealth of features included as part of the chip. Separate buses for instructions and data (Harvard architecture) allows simultaneous access of program and data, and overlapping of some operations for increased processing performance. The benefits of design simplicity are a very small chip, small pin count, and very low power consumption. PIC microcontrollers are rapidly gaining in popularity. They are being featured more and more often in construction projects in popular hobbyist magazines, and are chalking up a good number of design wins. Due to their low cost, small size, and low power consumption, these microcontrollers can now be used in areas that previously wouldn't have been appropriate (such as logic circuits). They are currently available in three lines: the PIC16C5x, PIC16Cxx, and PIC17Cxx families.
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Heinz Rongen Forschungszentrum Jülich, ZEL 52425 Jülich, Germany Tel: +49-(0)2461-614512 Fax: +49-(0)2461-613990 Email: [email protected] HD64180 (Hitachi) A powerful microcontroller with full Z80 functionality plus: extended memory management, two DMA channels, synchronous and asynchronous communications channels, timers, and interrupt controller. Some versions of this chip also include EPROM, RAM, and PIO (programmable input/output). It runs Z80 code in fewer clock cycles than the Z80 and adds in hardware multiply and a few other instructions.
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Heinz Rongen Forschungszentrum Jülich, ZEL 52425 Jülich, Germany Tel: +49-(0)2461-614512 Fax: +49-(0)2461-613990 Email: [email protected] TMPZ84C015B (Toshiba) A powerful microcontroller with full Z80 functionality plus: Counter/Timer, Serial I/O (SIO), Parallel I/O (PIO), Watchdog, Interrupt controller. It runs Z80 code in fewer clock cycles than the Z80 and adds in hardware multiply and a few other instructions.
Z8 (Zilog) A "loose" derivative of the Zilog Z80, the Z8 is actually a composite of several different architectures. Not really compatible with the Z80 peripherals. Has a unique architecture with three memory spaces: program memory, data memory, and a CPU register file. On-chip features include UART, timers, DMA, up to 40 I/O lines. Some versions include a synchronous/asynchronous serial channel. Features fast interrupt response with 37 interrupt sources. The Z8671 has Tiny Basic in ROM. The Super-8 is just that, a super version of the Z8 with more of everything.
5.2. Special Easy chips to use
MicroChip PIC '5x series With only 33 instructions, this chip is definitely easy to use! These chips simply need power, ground, and 1 of 4 different timing circuits. With I/O pins that are beefy (25mA per pin sink, 20mA per pin source) and drive both high and low, interfacing is super easy. It's great to hook LEDs and such directly to output pins with only a resister in-line!
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Heinz Rongen Forschungszentrum Jülich, ZEL 52425 Jülich, Germany Tel: +49-(0)2461-614512 Fax: +49-(0)2461-613990 Email: [email protected] 5.3. Intel 8052AH-BASIC This is a 8052 with internal 8 Kbytes Prom. The Prom already contains a Basic Interpreter. You can download high level Basic code from your host.
5.3.1. Inside the 8052-BASIC This chapter introduces you to the 8052-BASIC chip, including the kinds of projects you can do with it, what equipment, materials, and skills you need in order to design and build an 8052-BASIC project, and a pin-by-pin look at the chip and its abilities.
Possibilities The 8052-BASIC microcontroller is an easy-to-use, low-cost, and versatile computer- on-a-chip. It’s ideal for projects that require more than an assortment of logic gates, but less than a complete desktop computer system with a full keyboard, display, and disk drives. If you’re interested in doing more with computers than simply running applications programs, the 8052-BASIC gives you a chance to design and build a system from the ground up. With a few support chips and a program stored in memory, you can use the 8052-BASIC to sense, measure, and control processes, events, or conditions.
The 8052-BASIC is actually two products in one: it’s an 8052 microcontroller, with the BASIC-52 programming language on-chip. To begin using the 8052-BASIC, you need a minimum circuit consisting of the 8052-BASIC and some support components, plus a personal computer. This book contains specific instructions for use with “IBM- compatible,” or MS-DOS, computers, but you can use any computer that has an RS-232 serial port and communications software to go with it.
The Figure below shows the basic setup.
With an 8052-BASIC circuit connected by a serial link to a personal computer, you have a complete development system with these abilities: · You can write and run BASIC programs. You use the keyboard, video display, and other resources of the personal computer to type and view the programs and commands that the 8052-BASIC system executes. BASIC-52 is an interpreted language whose programs do not require an additional assembling or compiling step. You can run programs or execute commands immediately after you write them.
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Heinz Rongen Forschungszentrum Jülich, ZEL 52425 Jülich, Germany Tel: +49-(0)2461-614512 Fax: +49-(0)2461-613990 Email: [email protected] · You can use BASIC-52’s programming functions to permanently store your programs in EPROM or other nonvolatile memory. You don’t need a separate EPROM programmer. · You can also store programs on your personal computer’s disk. You can write or edit programs on your personal computer, and then upload them to the 8052- BASIC system. · To the basic circuits, you can add displays, switches, keypads, relays, and other components, depending on the needs of your project. · After program development, you can disconnect the link to the personal computer and let the 8052-BASIC system run its stored program on its own.
Limits No single product is ideal for every use. These are some of the limitations to the 8052-BASIC: ¨ Program execution can be slow, compared with programs that run on more powerful computers, or programs written in assembly language. A typical program line in BASIC-52 takes several milliseconds to execute. Because of this, there are some tasks that BASIC-52 just can’t handle—for example, detecting and responding to an interrupt within a few microseconds. But for many control, monitoring, and other tasks, BASIC-52 is fine. For example, a weather station that senses conditions once per minute and stores or displays the results doesn’t need super-fast response. And, if necessary, you can call an assembly-language routine for a portion of a program where speed is critical. Even if you write your programs in assembly language, C, or another language, you can use the 8052- BASIC system as a development system that enables you to upload your program to memory, run the program, and test and debug your programs and circuits. ¨ Another limitation of the 8052-BASIC is that a complete project requires additional components. If you’re looking for a true single-chip solution, the 8052-BASIC isn’t it. Even a minimal system requires an external RAM chip, and most systems also have an external EPROM or other non-volatile memory. The serial link and other optional functions also use some of the on-chip timers and input/output ports, so these may not be available for other uses. Still, the 8052-BASIC lets you to do a lot with a little. When needed, you can easily add chips to expand the input/output ports, timers, and other functions. ¨ And finally, don’t expect BASIC-52 to have the abilities of QBasic, Visual Basic or other BASIC programming languages that you may use on your personal computer. BASIC-52 is more capable than many other single-chip BASICs. It includes features like loops, subroutines, string handling, and even floating-point math for handling factional quantities. But there are some primitive aspects to the language. For example, the on-line editing functions are limited. Once you write a program line, you can change it only by retyping from the beginning. The limitations are understandable, because the entire programming language has to fit in the 8052’s 8 kilobytes of ROM. Fancy editing and other features just aren’t feasible in this small space.
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Heinz Rongen Forschungszentrum Jülich, ZEL 52425 Jülich, Germany Tel: +49-(0)2461-614512 Fax: +49-(0)2461-613990 Email: [email protected] There are solutions here as well. You can get around many of the editing limitations by writing and editing programs off-line, using your personal computer and text editor, and then uploading to the 8052-BASIC system. And, there are software and hardware products that enhance BASIC-52 and make it easier to use, especially for longer, more complex programming jobs.
5.3.2. The 8051 Family At the core of the 8052-BASIC is an 8052 microcontroller, a member of the 8051 microcontroller family. Intel Corporation introduced the 8051 in 1980. Since that time, 8051-family chips have been used as the base of thousands of products. Many other companies, including Philips, Siemens, Dallas Semiconductor, OKI, Fujitsu, and Harris-Matra now also make 8051-family chips. Some companies have expanded the 8051 family by offering compatible chips with additional features. Table below summarizes the differences among popular 8051-family chips. The 8052 is an enhanced 8051, with an extra timer and more RAM and ROM. The 8031 and 8032 are identical to the 8051 and 8052, except that the ROM area is unused, and program code must be stored in an external EPROM or other memory chip.
Differences among 8051-family chips.
Chip ProgramMem. Kilobyte RAM (bytes) Timers 8051 ROM 4 128 2 8052 ROM 8 256 3 8031 none - 128 2 8032 none - 256 3 8751 EPROM 4 128 2 8752 EPROM 8 256 3
· 80C51, 80C52, 80C31, and so on are CMOS versions of above. · 80C51FA/B/C add more versatile timers and an enhanced serial channel. · 8052-BASIC has the BASIC-52 programming language in ROM. · Packages include 40-pin DIP, 40-lead PLCC, and 44-pin QFP.
The 8052, like other 8051-family chips, is available in NMOS and CMOS versions.
5.4. Elements of the 8052 and 8052-BASIC These are the major elements of the 8052, plus the enhancements included in the 8052-BASIC:
CPU The CPU, or central processing unit, executes program instructions. Types of instructions include arithmetic (addition, subtraction), logic (AND, OR, NOT), data transfer (move), and program branching (jump) operations. An external crystal provides a timing reference for clocking the CPU.
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Heinz Rongen Forschungszentrum Jülich, ZEL 52425 Jülich, Germany Tel: +49-(0)2461-614512 Fax: +49-(0)2461-613990 Email: [email protected] ROM ROM (read-only memory) is the read-only memory that is programmed into the chip in the manufacturing process. In the 8052-BASIC, the ROM contains the BASIC-52 interpreter program that the 8052 executes on boot-up. As far as the hardware is concerned, this is the only difference between the ordinary 8052 and the 8052-BASIC.
RAM RAM (random-access memory) is where programs store information for temporary use. Unlike ROM, the CPU can write to RAM as well as read it. Any information stored in RAM is lost when power is removed from the chip. The 8052 has 256 bytes of RAM. BASIC-52 uses much of this for its own operations, with a few bytes available to users.
I/O Ports I/O (Input/Output) Ports enable the 8052 to read and write to external memory and other components. The 8052 has four 8-bit I/O ports (Ports 0-3). As the name suggests, the ports can act as inputs (to be read) or outputs (to be written to). Many of the port bits have optional, alternate functions relating to accessing external memory, using the on-chip timer/counters, detecting external interrupts, and handling serial communications. BASIC-52 assigns alternate functions to the remaining port bits. Some of these functions are required by BASIC-52, while others are optional. If you don’t use an alternate function, you can use the bit for any control, monitoring, or other purpose in your application.
Accessing external memory. The largest alternate use of the ports has to do with accessing external memory. Although the 8052 is a single-chip computer, a complete 8052-BASIC system requires additional components. It must have external RAM in addition to the 8052’s internal RAM, and most systems also have EPROM, EEPROM, or battery-backed RAM for permanent storage of BASIC-52 programs. Accessing this external memory uses all of Ports 0 and 2, plus bits 6 and 7 of Port 3, to hold data, addresses, and control signals for reading and writing to external memory. Data here refers to a byte to be read or written, and may be any type of information, including program code. The address defines the location in memory to be read or written. During a memory access, Port 0’s eight pins (AD0-AD7) first hold the lower byte of the address, followed by the data to be read or written. This method of carrying both addresses and data on the same signal lines is called a multiplexed address/data bus. It’s a popular arrangement that many devices use, since it requires fewer pins on the chip, compared to giving each data and address line its own pin. Port 2’s eight lines hold the higher byte of the address to be read or written to. These lines make up the high address bus (A8-A15). Together, the 16 address lines can access 64 kilobytes (65,536 bytes) of memory, from 00000000 00000000 to 11111111 11111111 in binary, or 0000h to FFFFh in hexadecimal. Besides pins to hold the data and addresses, the 8052 must also provide control signals to initiate the read and write operations. Control signals include WR (write), RD (read), PSEN (program store enable), and ALE (address latch enable). Some of the address lines
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Heinz Rongen Forschungszentrum Jülich, ZEL 52425 Jülich, Germany Tel: +49-(0)2461-614512 Fax: +49-(0)2461-613990 Email: [email protected] may also function as control signals that help to select a chip during a memory access.
Code and data memory. To understand the operation of the control signals, you need to know a little about how the 8052 distinguishes between two types of memory: data and code, or program, memory. By using different control signals for each type of memory, the 8052 can access two separate 64K areas of memory, with each addressed from 0000h to FFFFh, and each using the same data and address lines. The 8052 accesses code memory when it executes an assembly-language program or subroutine. Code memory is read-only; you can’t write to it. The only instructions that access code memory are read operations. Code memory is intended for programs or subroutines that have been previously programmed into ROM or EPROM. The 8052 strobes, or pulses, PSEN when it accesses external code memory. Accesses to internal code memory (the BASIC-52 interpreter in ROM) do not use PSEN or any external control signals. Data memory is read/write memory, usually RAM. Instructions that read data memory strobe RD, and instructions that write to data memory strobe WR. The termdata memory may be misleading, because it can hold any information that is accessed with instructions that strobe RD or WR. In fact, BASIC-52 programs are stored in data memory, not code memory as you might think. This is because the 8052 does not execute the BASIC programs directly. Instead, the BASIC-52 interpreter program reads the BASIC programs as data and then translates them to machine code for execution by the 8052. If you don’t need all of the available memory space, you can combine code and data memory in a single area. With combined memory, WR controls write operations, and PSEN and RD are logically ANDed to create a read signal that is active when either PSEN or RD is low. Combined data/code memory is handy if you want the flexibility to store either BASIC or assembly-language programs in the same chip, or if you want to be able to upload assembly-language routines into RAM for testing. ALE is the final control signal for accessing external memory. It controls an external latch that stores the lower address byte during memory accesses. When the 8052 reads or writes to external memory, it places the lower address byte on AD0-AD7 and strobes ALE, which causes the external latch to save the lower address byte for the rest of the read or write cycle. After a short delay, the 8052 replaces the address on AD0-AD7 with the data to be written or read.
Timers and Counters. The 8052 has three 16-bit timer/counters, which make it easy to generate periodic signals or count signal transitions. BASIC-52 assigns optional functions for each of the timer/counters. Timer 0 controls a real-time clock that increments every 5 milliseconds. You can use this clock to time events that occur at regular intervals, or as the base for clock or calendar functions. Timer 1 has several uses in BASIC-52, including controlling a pulse-width-modu-lated output (PWM) (a series of pulses of programmable width and number); writing to a line Inside the 8052-BASIC printer or other serial peripheral (LPT); and generating pulses for EPROM programming (PGM PULSE). Timer 2 generates a baud rate for serial communications at SER IN and SER OUT. These are all typical applications for timer/counters in microcontroller circuits. If you don’t use the optional timer functions, you can program the timers for other applications. In addition to timing functions, Microcontroller (36)
Heinz Rongen Forschungszentrum Jülich, ZEL 52425 Jülich, Germany Tel: +49-(0)2461-614512 Fax: +49-(0)2461-613990 Email: [email protected] where the timer increments at a defined rate, you can use the timers for event counting, where the timer increments on an external trigger and measures the time between triggers. If you use the timers for event counting, T2, T2(EX), T0, and T1 detect transitions to be counted.
The serial port. The 8052’s serial port automatically takes care of many of the details of serial communications. On the transmit side, the serial port translates bytes to be sent into serial data, including adding start and stop bits and writing the data in a timed sequence to SER OUT. On the receive side, the serial port accepts serial data at SER IN and sets a flag to indicate that a byte has been received. BASIC-52 uses the serial port for communicating with a host computer.
External interrupts. INT0 and INT1 are external interrupt inputs, which detect logic levels or transitions that interrupt the CPU and cause it to branch to a predefined program location. BASIC-52 uses INT0 for its optional direct-memory-access (DMA) function.
Programming functions. BASIC-52’s programming commands use three additional port bits (ALEDIS, PGM PULSE, and PGM EN) to control programming voltages and timing for storing BASIC-52 programs in EPROM or other nonvolatile memory. Additional Control Inputs Two additional control inputs need to be mentioned. A logic high on RESET resets the chip and causes it to begin executing the program that begins at 0 in code memory. In the 8052-BASIC chip, this program is the BASIC-52 interpreter. EA (external memory access) determines whether the chip will access internal or external code memory in the area from 0 to 1FFFh. In BASIC-52 systems, EA is tied high so that the chip runs the BASIC interpreter in internal ROM on boot- up.
Power Supply Connections And, finally, the chip has two pins for connecting to a +5-volt DC power supply (VCC) and ground (VSS). That finishes our tour of the 8052-BASIC chip. We’re now ready to put together a working system.
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Heinz Rongen Forschungszentrum Jülich, ZEL 52425 Jülich, Germany Tel: +49-(0)2461-614512 Fax: +49-(0)2461-613990 Email: [email protected] 6. Special microcontroller features
Inside of a microcontroller are special function building blocks which makes the different controllers the best choice for different applications. These special functions could be:
Watchdog timer A watchdog timer provides a means of graceful recovery from a system problem. This could be a program that goes into an endless loop, or a hardware problem that prevents the program from operating correctly. If the program fails to reset the watchdog at some predetermined interval, a hardware reset will be initiated. The bug may still exist, but at least the system has a way to recover. This is especially useful for unattended systems.
Idle/Halt/Wakeup The device can be placed into IDLE/HALT mode by software control. In both Halt and Idle conditions the state of the microcontroller remains. RAM is not cleared and any outputs are not changed. The terms idle and halt often have different definitions, depending on the manufacturer. In IDLE mode, all activities are stopped except: · associated on-board oscillator circuitry · watchdog logic (if any) · the clock monitor · the idle timer (a free running timer) Power supply requirements on the microcontroller in this mode are typically around 30% of normal power requirements of the microprocessor. Idle mode is exited by a reset, or some other stimulus (such as timer interrupt, serial port, etc.). A special timer/counter (the idle timer) causes the chip to wake up at a regular interval to check if things are OK. The chip then goes back to sleep.
In Halt mode, all activities are stopped (including timers and counters). The only way to wake up is by a reset or device interrupt (such as an I/O port). The power requirements of the device are minimal and the applied voltage (Vcc) can sometimes be decreased below operating voltage without altering the state (RAM/Outputs) of the device. Current consumption is typically less than 1 uA.
6.1. Peripheral I/O
UART A UART (Universal Asynchronous Receiver Transmitter) is a serial port adapter for asynchronous serial communications.
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Heinz Rongen Forschungszentrum Jülich, ZEL 52425 Jülich, Germany Tel: +49-(0)2461-614512 Fax: +49-(0)2461-613990 Email: [email protected] USART A USART (Universal Synchronous/Asynchronous Receiver Transmitter) is a serial port adapter for either asynchronous or synchronous serial communications. Communications using a USART are typically much faster (as much as 16 times) than with a UART.
Synchronous serial port A synchronous serial port doesn't require start/stop bits and can operate at much higher clock rates than an asynchronous serial port. Used to communicate with high speed devices such as memory servers, display drivers, additional A/D ports, etc. Can also be used to implement a simple microcontroller network.
Analog to Digital Conversion (ADC) Converts an external analog signal (typically relative to voltage) and converts it to a digital representation. Microcontrollers that have this feature can be used for instrumentation, environmental data logging, or any application that lives in an analog world.
Digital to Analog Converters (DAC) This feature takes a Digital number and converts it to a analog output. The number 50 would be changed to the analog output of (50/256 * 5Volts) = .9765625V on a 8- bit / 5 Volt system.
Pulse width modulator Often used as a digital-to-analog conversion technique. A pulse train is generated and regulated with a low-pass filter to generate a voltage proportional to the duty cycle.
Pulse accumulator A pulse accumulator is an event counter. Each pulse increments the pulse accumulator register, recording the number of times this event has occurred.
I2C bus - Inter-Integrated Circuit bus (Philips) The I2C bus is a simple 2 wire serial interface developed by Philips. It was developed for 8 bit applications and is widely used in consumer electronics, automotive and industrial applications. In addition to microcontrollers, several peripherals also exist that support the I2C bus. The I2C bus is a two line, multi-master, multi-slave network interface with collision detection. Up to 128 devices can exist on the network and they can be spread out over 10 meters. Each node (microcontroller or peripheral) may initiate a message, and then transmit or receive data. The two lines of the network consist of the serial data line and the serial clock line. Each node on the network has a unique address which accompanies any message passed between nodes. Since only 2 wires are needed, it is easy to interconnect a number of devices.
CAN
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Heinz Rongen Forschungszentrum Jülich, ZEL 52425 Jülich, Germany Tel: +49-(0)2461-614512 Fax: +49-(0)2461-613990 Email: [email protected] CAN (Controller Area Network) is a multiplexed wiring scheme that was developed jointly by Bosch and Intel for wiring in automobiles. The CAN specification seems to be the one that is being used in industrial control both in North American and Europe. With lower cost microcontrollers that support CAN, CAN has a good potential to take off.
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Heinz Rongen Forschungszentrum Jülich, ZEL 52425 Jülich, Germany Tel: +49-(0)2461-614512 Fax: +49-(0)2461-613990 Email: [email protected] 6.2. Advanced Memory options
EEPROM - Electrically Erasable Programmable Read Only Memory Many microcontrollers have limited amounts of EEPROM on the chip. EEPROM seems more suited (because of its economics) for small amounts of memory that hold a limited number of parameters that may have to be changed from time to time. This type of memory is relatively slow, and the number of erase/write cycles allowed in its lifetime is limited.
FLASH (EPROM) Flash provides a good better solution than regular EEPROM when there is a requirement for large amounts of non-volatile program memory. It is both faster and permits more erase/write cycles than EEPROM.
Battery backed-up static RAM Battery backed-up static RAM is useful when a large non-volatile program and DATA space is required. A major advantage of static RAM is that it is much faster than other types of non-volatile memory so it is well suited for high performance application. There also are no limits as to the number of times that it may be written to so it is perfect for applications that keep and manipulate large amounts of data locally.
OTP - One Time Programmable (PROM) An OTP is a PROM (Programmable Read-Only-Memory) device. Once your program is written into the device with a standard EPROM programmer, it can not be erased or modified. This is usually used for limited production runs before a ROM mask is done in order to test code. A OTP (One Time Programmable) part uses standard EPROM, but the package has no window for erasing.
Software protection Either by encryption or fuse protection, the programmed software is protected against unauthorized snooping (reverse engineering, modifications, piracy, etc.).
6.3. Power Management and Low Voltage
Low voltage parts In the recent past, as consumer goods are beginning to drive major segments of the microcontroller market, and as consumer goods become portable and lightweight, the requirement for 3 volt (and lower) microcontrollers has become urgent (3 volts = 2 battery solution / lower voltage = longer battery life). Most low voltage parts in the market today are simply 5 volt parts that were modified to operate at 3 volts (usually at a performance loss). Some micros being released now are designed from the ground up to operate properly at 3.0 (and lower) voltages, which offer comparable performance of the 5 volt devices.
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Heinz Rongen Forschungszentrum Jülich, ZEL 52425 Jülich, Germany Tel: +49-(0)2461-614512 Fax: +49-(0)2461-613990 Email: [email protected] There are a few interesting rules of thumb regarding transistors: 1) The amount of power they dissipate is proportional to their size. If you make a transistor half as big, it dissipates half as much power. 2) Their propagation delay is proportional to their size. If you make a transistor half as big, it's twice as fast. 3) Their cost is proportional to the square of their size. If you make them half as big, they cost one quarter as much.
If you make a transistor smaller, you improve the power, speed, and cost. The only drawback is that they are harder to make. Everybody in the world wants to make transistors smaller and smaller, the advantages are enormous. For years people have been using 5 Volts to power IC's. Because the transistors were large, there was little danger damaging the transistor putting this voltage across it. However, now that the transistors are getting so small, 5 Volts will actually fry them. The only way around this is to start lowering the voltage. This is why people are now using 3 (actually 3.3) Volt logic, and lower in the next few years. It isn't just because of batteries.
Interrupts
Polling Polling is not really a "feature" - it's what you have to do if your microcontroller of choice does not have interrupts. Polling is a software technique whereby the controller continually asks a peripheral if it needs servicing. The peripheral sets a flag when it has data ready for transferring to the controller, which the controller notices on its next poll. Several such peripherals can be polled in succession, with the controller jumping to different software routines, depending on which flags have been set.
Interrupts Rather than have the microcontroller continually polling - that is, asking peripherals (timers / UARTS / A/Ds / external components) whether they have any data available (and finding most of the time they do not), a more efficient method is to have the peripherals tell the controller when they have data ready. The controller can be carrying out its normal function, only responding to peripherals when there is data to respond to. On receipt of an interrupt, the controller suspends its current operation, identifies the interrupting peripheral, then jumps (vectors) to the appropriate interrupt service routine. The advantage of interrupts, compared with polling, is the speed of response to external events and reduced software overhead (of continually asking peripherals if they have any data ready). Most microcontrollers have at least one external interrupt, which can be edge selectible (rising or falling) or level triggered. Both systems (edge/level) have advantages. Edge - is not time sensitive, but it is susceptible to glitches. Level - must be held high (or low) for a specific duration (which can be a pain - but is not susceptible to glitches).
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Heinz Rongen Forschungszentrum Jülich, ZEL 52425 Jülich, Germany Tel: +49-(0)2461-614512 Fax: +49-(0)2461-613990 Email: [email protected] Microcontroller (43)
Heinz Rongen Forschungszentrum Jülich, ZEL 52425 Jülich, Germany Tel: +49-(0)2461-614512 Fax: +49-(0)2461-613990 Email: [email protected] 7. Writing the Control Program When it’s time to write the program that controls your project, the options include using machine code, assembly language, or a higher-level language. Which programming language you use depends on things like desired execution speed, program length, and convenience, as well as what’s available in your price range.
Machine code. The most fundamental program form is machine code, the binary instructions that cause the CPU to perform the operations you desire.
7.1. Assembly language. One step removed from machine code is assembly language, where abbreviations called mnemonics (memory aids) substitute for the machine codes. The mnemonics are easier to remember than the machine codes they stand for. For example, in the 8052’s assembly language, the mnemonic CLR C means clear the carry bit, and is easier to remember than its binary code (11000011). Since machine code is ultimately the only language that a CPU understands, you need some way of translating assembly-language programs into machine code. For very short programs, you can hand assemble, or translate the mnemonics yourself by looking up the machine codes for each abbreviation. Another option is to use an assembler, which is software that runs on a desktop computer and translates the mnemonics into machine code. Most assemblers provide other features, such as formatting the program code and creating a listing that shows both the machine-code and assembly-language versions of a program side -by-side.
7.2. Higher-level languages. A disadvantage to assembly language is that each device family has its own set of mnemonics, so you have to learn a new vocabulary for each family you work with. To get around this problem, higher-level languages like C, Pascal, Fortran, Forth, and BASIC follow a standard syntax so that programs are more portable from one device to another. The idea is that with minor changes, you can use a language like BASIC to write programs for many different devices. In reality, each language tends to develop many different dialects, depending on the chip and the preferences of the language’s vendor, so porting a program to a different device isn’t always effortless. But there are many similarities among the dialects of a single language, so, as with spoken language, a new dialect is easier to learn than a whole new language. Higher-level languages also simplify programming by allowing you to do in one or a few lines what would require many lines of assembly code to accomplish.
Interpreters and compilers are two forms of higher-level languages. An interpreter trans-lates program into machine code each time the program runs, while a compiler translates nly once, creating a new, executable file that the computer runs directly, without re-trans-lating. As a rule, interpreters are very convenient for shorter programs where execution speed isn’t critical. With an interpreted language, you can run your program code immediately after you write it, without a separate compile or
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Heinz Rongen Forschungszentrum Jülich, ZEL 52425 Jülich, Germany Tel: +49-(0)2461-614512 Fax: +49-(0)2461-613990 Email: [email protected] assembly step. A compiler is a good choice when a program is long or has to execute quickly. A single language like BASIC may be available in both interpreted and compiled versions. Each device family requires its own interpreter or compiler to translate the higher-level code into the machine code for that device. In other words, you can’t use QuickBASIC for IBM PCs to program an 8052 microcontroller—you need a compiler that generates program code for the 8052. Compared to an equivalent program written in assembly language, a compiled program usually is larger and slower, so assembly language is the way to go if a program must be as fast or as small as possible. A higher-level language also may not offer all of the abilities of assembly code, though you can get around this by calling subroutines in assembly language when necessary.
BASIC-52 is an interpreted language, but BASIC compilers for the 8052 are also available. In fact, you can have the best of both worlds by testing your programs with the BASIC-52 interpreter, and compiling the finished product for faster execution and other benefits of the compiled version.
8. Testing and Debugging After you’ve written a program, or a section of one, it’s time to test it and as necessary, find and correct mistakes to get it working properly. The process of ferreting out and correcting mistakes is called debugging. Easy debugging and troubleshooting can make a big difference in how long it takes to get a system up and running. As with programming, you have several options here as well.
8.1. Testing in EPROM. One way is to burn your program into EPROM, install the EPROM in your system, run the program, and observe the results. If problems occur (as they usually will) you modify the program, erase and reburn the EPROM, and try again, repeating as many times as necessary until the system is operating properly.
8.2. Development systems. Another option is to use a development system. A typical development system consists of a monitor program, which is a program stored in EPROM or other memory in the microcontroller system, and a serial link to a personal computer. Using the abilities of the monitor program, you can load your program from a personal computer into RAM (instead of the more permanent EPROM) on the microcontroller system, then run the program, modify it, and retry as often as necessary until the program is working properly. Most development systems also allow single-stepping, setting breakpoints, and viewing and changing the data in memory. In single-stepping, you run the program one step at time, pausing after each step, so you can more easily monitor what the circuits and program are doing at each step. A breakpoint is a program location where the program stops executing and waits for a command to continue. You can set breakpoints at critical spots in your program. At any breakpoint, you can view or change the contents of memory or perform other tests.
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Heinz Rongen Forschungszentrum Jülich, ZEL 52425 Jülich, Germany Tel: +49-(0)2461-614512 Fax: +49-(0)2461-613990 Email: [email protected] 8.3. The 8052-BASIC’s development system The 8052-BASIC system and a personal computer form a complete development system for writing, testing, and storing programs. The personal computer’s keyboard and screen make it easy to write and run programs and view the results. BASIC-52 has many built-in debugging features that make it easy to test programs. You can run a program immediately after writing it, without having to assemble, compile, or program an EPROM. You can use a STOP statement and CONT (continue) command to set breakpoints and resume executing your program. You can use PRINT statements to display variables as the program runs. And, if you wish, you can use your personal computer for writing programs off-line and uploading and downloading them to the 8052-BASIC system.
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Heinz Rongen Forschungszentrum Jülich, ZEL 52425 Jülich, Germany Tel: +49-(0)2461-614512 Fax: +49-(0)2461-613990 Email: [email protected]