P·R·Q·D·U·C·T P·R·E·V·I·E·W ...J W <: I U ~ 10 o w I Cl. <: '"<.) § I Cl. BY GREGG WILLIAMS, JON EDWARDS, AND PHILLIP ROBINSON BY T E 83 THE AMIGA IN BRIEF Name Amiga Personal Computer Manufacturer Commodore International not coinC identally, people want Apple 1200 Wilson Dr. to increase the Mac's speed, add West Chester, PA 19380 color. and lower its price. (215) 431-9100 Commodore has just introduced a Price computer that promises these im­ $1295 provements, and it does so by doing many things in hardware At S1295 . Microprocessor Motorola 68000, a 32-/16-bit microprocessor (32-bit internal data path and the Amiga Personal Computer (see registers, 16-bit external data bus) running at 7.15909 MHz photo I) promises lightning-fast desktop-metaphor graphics in color Main Memory and twice as much memory and disk 256K bytes dynamic RAM , user-expandable to 512K bytes; machine's design allows for maximum of 8.5 megabytes storage as the Macintosh for several hundred dollars less than the Macin­ ROM tosh (about S900, but you'll have to 192K bytes of ROM containing multitasking, graphics, sound, buy a monitor or television set for the and animation support routines Amiga). It also has an expansion bus Graphics and a whopping 192 K bytes of so­ Five modes (320 by 200 pixels, 32 colors; 320 by 400, 32 colors; 640 phisticated 68000 code in ROM (read­ by 200, 16 colors; 640 by 400, 16 colors; sample-and-hold mode); only memory) that extends the multi­ independent horizontal and vertical scrolling of dual playfields; eight hardware sprites; colors chosen from a palette of 4096 colors tasking, graphics, sound, and anima­ tion capabilities of the Amiga Sound hardware. Four independent audio channels; sound produced without supervision of 68000 SYSTEM DESCRIPTION Floppy Disk The Amiga is summarized in the In Built-in 3V2-inch double-sided disk drive. Disks hold 880K bytes Brief section on this page. It has no in 160 tracks, each with eleven 512 -byte sectors; drive hardware can read slots for expansion cards, but Com­ an entire track at a time modore later intends to offer a box Keyboard that connects to the expansion con­ Detached 89-key keyboard with calculator pad, function and cursor keys; nector to add several expansion slots. keyboard returns row/column keycodes for each key, sends both key-up and (It is theoretically possible to add key-down signals; can sense up to two keys simultaneously; 8 8-key type-ahead buHer megabytes of memory in this way.) The Amiga's disk operating system Expansion Ports will also be able to look at the expan­ Disk port onto which three additional disk drives can connect via daisy chain; sion box, determine what peripherals serial port with maximum transfer rate of 500,000 bps; programmable parallel port normally configured as Centronics-compatible; are present. and configure itself ac­ expansion bus includes full set of signals for optional peripherals and cordingly. regardless of the box 's memory expansion contents. User Interface (Intuition) Supports multitasking through the use of virtual terminals; allows simultaneous SYSTEM ARCHITECTURE display of diHerent resolutions and graphics modes The Amiga has a unique architecture that is only partially described by a Bundled Software functional block diagram (see figure AmigaDOS Voice Synthesis Library I) Three custom chips relieve the ABasiC 68000 processor of many tasks that Tutorial (Mindscape) tie it down in other computers. How­ Kaleidoscope (Electronic Arts) ever, the diagram does not show the Audio and Video Ports finely tuned sharing of the system's Two stereo audio jacks; RGB analog, RGB digital, and NTSC composite data and address buses, the 25 DMA output Miscellaneous Gregg Williams is a senior technical editor at Three custom chips to control graphics, audio, and peripheral I/O; chips BYTE, and Jon Edwards is a technical editor. connected by 19-bit register-address bus; two-button mechanical mouse They can be reached at BYTE, POB 372. Han cock. NH 03449. Phillip Robinson is Optional Peripherals 3'l2-inch 880K-byte disk drive; RGB analog color monitor; 256K-byte memory a West Coast sen ior technica l editor at BYTE. expansion module; 300/1200-bps modem; MIDI interface; frame grabber He can be reached at BYTE M~gazine . 425 Battery St .. San Francisco. CA 94111. 84 B Y T E • AUGUST 1985 THE AMIGA (direct memory access) channels that • The graphics custom chip. which data buses with 25 channels of DMA. do many data-movement-intensive manipulates the visible display. per­ the registers and logic of which reside operations without tying up the mits up to two independent bit­ in the custom chips. Amiga's DMA is 68000. or the multiprocessing mapped images and eight sprites fast for two reasons: first. the fact that routines in ROM that allow the Amiga (which are images that can be moved each device has its own DMA chan­ to orchestrate a variety of tasks. In the easily around the screen. "under" or nel decreases the overhead asso­ following sections we will look at the "on top of" the bit-mapped images). ciated with a DMA operation; second. key elements of the Amiga's system • The peripherals/sound custom chip many DMA operations are interleaved architecture. contains four channels of sound. the with 68000 bus access in a way that disk controller. an interrupt controller. makes the DMA transparent to the and the interfaces for the serial port THE CUSTOM CHIPS 68000 (see below for details). and the mouse/joystick port. When DMA occurs between mem­ The three custom chips that control ory- and custom-chip registers. the DMA. graphics. sound. and I/O (input/ INTERRUPTS AND DMA use of the 19-bit register-address bu s output) (see photo 2) were designed In the Amiga. all the peripherals are (see figure I) makes the transfer twice by Jay Miner. who is best known for interrupt-driven-that is. the 68000 is as fast. By putting the memory ad­ his design of the custom chips in the not tied up constantly polling them to dress on the address bus and the Atari 800 series computers. Although see if they have new data; instead. the register address on the register­ we will discuss them in depth by func­ 68000 gets data from the peripheral address bus. the DMA circuitry causes tion. here is a simple breakdown: only when the peripheral sends an in­ the data value to move directly from • The "animation custom chip" actual­ terrupt signal. The peripherals/sound the memory address to the register. ly contains several miscellaneous chip receives interrupt-request signals This occurs twice as fast as DMA functions. It is the "traffic cop" that from one of 15 sources (e.g .. the disk would via the 68000. which would controls DMA. It contains the Copper. drive or a sound channel). translates first read the data into itself and then a coprocessor that can directly con­ the request to one of six interrupt write the result to the register. trol the other chips in relation to the levels supported by the 68000 (the video beam. and the Blitter. a device seventh is reserved for future use). LIBRARIES AND DEVICES that quickly draws lines. fills areas with and sends the interrupt signal to the System software (much of it in the a given color. and manipulates rec­ 68000. 192 K bytes of ROM) contains libraries. tangular blocks of pixels. The 68000 shares the address and (continued ) --TV----RG8-COMPOSITE--- VIDEO GAME 1/0 1/0 AUDIO PRINTER PORT CHIP MEMORY 256K BYTES STANDARO 256K BYTES ADD-ON Figure I: A block diagram of the Amiga Personal Computer. AUGUST 1985 • BY T E 85 Composite Audio out video out Connector to RF modulator RGB Serial External Parallel Keyboard video out n interface disk interface interface connector processor 256K Locations dynamic RAM Display for ROMs Animation bu s arbitration, 8520s custom chip RAM support, and bus drivers Graphics custom chip Photo 2: Tlie Amiga motlierboa rd. Tlie internal disk drive. wliicli lias been removed. would normall y obscure tlie lower riglit corner of tlie motlierboard Tlie power supply (not sliown) is to tlie left of tlie motlierboard. 86 BY T E • AUGUST 1985 THE AMIGA a predefined way of organizing useful DMA (enough to show a 16-color low­ routines so that they can be accessed The Exec routines re solution image). The DMA ci rcuits with maximum flexibility. Libraries perform many on each ch ip "know" when th eir slots can be resident or transient and can occur on each hori zo ntal line and be used at any memory address functions vital automaticall y initiate the DMA trans­ (when they're in RAM [random-access fer without involving the 68000. readlwrite memoryf). Both routines to the operation In many cases, the Copper and the and data can always be ca lled via a Blitter aren't active, leav ing the 68000 68000 indirect reference with offset; of the Amiga. running at fu ll speed (Actually. some this all ows you to write code using a in structions need the bus at odd library routine without knowing that tasks will execute. Tasks with identical times: if the bus isn't avai lable. th e library's address at compile time. (In numbers share the Amiga in time 68000 will in sert wa it states until the fact. all the code in the system can be sli ces of preselected duration. A tas k bus-arbitration PAL [programmed­ refe renced knowing only one fixed wi th higher priority preempts the cur­ array logic chip[ signals th at th e bus address in the machine, and even that rent task and begins executing.