THE MAGAZINE FOR NEW IDEAS IN ELECTRONICS wild this 650 COMPUTER ln one board experiment with UNCTION GENERATOR ew Exar IC for your phone BUILD TELESWITCH and turn things on SIGNE TICS 2650 MICFOPP(iCE"pb IC data sheet ASCII ENCCQ►ED► YEYEOARI► E6-CHARACTEF EY 16-LINE,UIUE0 DISPLAY CI,,, `ETICON SAD-1024 CASSETTE ";'_FFACE--trii!~r SiANIiAFD NT . SUPERVISCi; E.:,,_ .' bucket-brigade 1024 2098 SfiE'E installing I/O PORTS E' : :_: SIN6LE BROUC;',? ANTENNA TOWE RADIE-E_E. : :an be easy AND JEFF
• * Lab-Tested Hi-Fi Reports GERNSBACK Yamaha (T-800 Tuner & Kenwood KR7600 Receiver State-Of-Solid-State * Equipment Reports * Reader Questions COMPUTER PROJECT
._~ Build 2650-Based ~~ ) ; , ~: Microcomputer _ ~i;` system =
Part I. Built on a single printed-circuit board, this 2650 microcomputer contains a video and cassette tape interface and resident supervisor program. Add a keyboard, video monitor, cassette tape recorder and power supply for a complete working system
JEFF ROLOFF SPECIFICATIONS AN EASY-TO-USE COMPUTER SYSTEM MUST have essentially four major sections. DISPLAY GENERATOR There is, of course. the actual processing Display Format: 16 lines of 80 characters. User programmable character generator section that usually (at least for small selected by setting bit 6 of the stored data to logic-1 level. Bit 7 available for any users) contains a microprocessor IC. special user application. There must also be input and output Method of Accessing: The processor writes correct RAM location to place a sections so that the processor can character on the screen. communicate with the outside world. Output: Composite video, 1 volt P-P nominal, 75 ohms. 7.1 Mhz. The last section that is essential for a computer's operation is the memory. Cursor: Written by processor just like any other character. Supervisor uses a square This is used to store programs and data. dot centered in character field. and it can be either a memory that Screen Blanking: During horizontal or vertical retrace, between character lines and needs to be accessed very quickly when whenever the processor is accessing the display memory. running a program or a memory used to Display Addressing: Starts (upper left hand corner) at address H1000, and ends at store information for long periods of H14FF. As addresses are incremented, the display position moves downward. time, such as cassette tape. Additional User RAM: A total of 768 bytes starting at address H1500. Actually a part The 2650 computer project presented of the display memory, but this is transparent to the user. here has all of the above circuits mounted on a single printed-circuit PROCESSOR board. In addition, there is a versatile supervisor program that allows you to Type: Signetics 2650 microprocessor. easily create your own programs. The Buffering: All processor signals buffered for TTL fan-out of 10. heart of the unit is the Signetics 2650 Memory: 1K bytes of PROM which contains supervisor program. 768 bytes of RAM microprocessor. Basically, it is a simple • unused by display is available for user programs. PROM is on-board expandable to to use microprocessor with a powerful 4K bytes. instruction set. The input device can be Control Lines: Pause and stop-clock lines allow single stepping of programs. any ASCII-encoded keyboard, which Disable-lines for address data, and control buses to allow DMA (Direct Memory simply hooks to an input port of the Access) or dual processor operation. computer. The output device is a high quality 80-character by 16-line video CASSETTE INTERFACE display generator which is fully con-
Recording Format: 300 baud, 1200/2400-Hz Kansas City Standard. trolled by the processor. There are also parallel input and output ports (one Output Voltage: 100 mV P-P. liadv
each) to allow you to communicate with Misc. Size: 8'/2-inch square printed-circuit board. ►
any other peripheral device, such as a s Power Consumption: 3 amps at 5 volts. line printer or a floppy disc. The «
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