Cosmic Cabdrivers' Guide to the Universe Presents:
The 8-bit ATARI with 64 k ram was a better and more efficient computer than
IBM compatibles built years afterward. it takes a 486 with vga
and a sound card just to emulate the graphics, sound, and speed capabilties
of an unadorned 800.
However, in the age of multiple competing and mutually incompatible systems, someone had to win. IBM had the name, and they cleverly impressed
the unaware with large, heavy steel cases and noisy power-supply fans.
Syzygy, from the japanese strategy game go,
which means the straight-line configuration between three
celestial bodies,was the 3 founders' first choice to name the
That name had been taken, however. atari was one of three words chosen.
It means check.
The other two were sente, (the upper hand) and
hanne, (acknowledge an over-taking move). The founders,
Nolan Bushnell, Ted Dabney and Larry Bryan, often played go.
Though now considered obsolete by those who feel they must have the latest
hardware, atari 8-bit computers, 400, 800, 800xl, 1200xl, etc. , are quite useful and
easy to set up and use. They can often be found in thrift stores and garage
sales quite cheaply, and they are usually still operational.
Although both color and monochrome monitors are available for them,
any television set can be used. because of this, Ataris are handy for inserting
titles or graphics into home videos.
Unlike the heavy, noisy pc's, ataris are light, compact, and silent. the external disk
drives have a unique clatter while reading or writing but are quiet on standby.
16k ram, 4 joyports, 1 eprom rom cartridge slot, 9 volts ac, membrane keyboard
48k, 4 joyports, 2 cartridge slots, 9 v ac, typewriter style
1200XL 64k, 2 joyports, 1 cartridge slot, 9 v ac, slim design,
function keys, international character set added
600XL 48k, 2 joyports, 1 cartridge slot, ROM basic, 5 v dc, parallel expansion slot
800XL 64k, 2 joyports, 1 cartridge slot, ROM basic, 5 v dc,
late 800XL with a redesigned motherboard, plus the FREDDY
chip,5 v dc
65.5k, 2 joyports, 1 cartridge slot, ROM basic, 5 v dc
65.5k, 8 sound channels; same as 65XE plus AMIE/AMY sound chip, 5 v dc
same as 65XE plus 3.5 inch floppy drive, 5 inch green monitor built
128k, 2 joyports, ROM Basic, midi port, 5 v dc
same as 800XL plus modem and speech synthesizer....(looks like a
1200XL)... 5v dc/12 v dc
same as 1400XL plus room for 2 internal 5.25 inch drives...(controller not included)
same as 1400XL plus 5.25 inch floppy drive (Epson SD521 360K disk
drives)...5 v dc/12 v dc
Amiga/Amiga-like. Now appears that 1850XLD was the model name for
1650XLD used 1450XLD case and 1200XL keyboard
1850XLD Mickey Atari clone of the Amiga Lorraine
Using bank-switching techniques, one can up RAM to 128k, 256 k, or more)
However, since less memory is wasted in atari programming, 64 k is usually plenty.
power suppliesThe 400, 800, and 1200xl used a 9v ac external
transformer with a two-conductor plug. The rest of the xl's, except as noted,
used a 5 volt dc external power supply. It connects via a din plug.
The 850 disk drives use 9 volts ac, with the same connector as the 400/800
computer, but require a higher power output. if your drives don't work right
you may be starving them with lower-wattage power supplies.
I built a 12-volt auto dc to 5volt dc converter for my 800xl, using a 12-volt
portable tv as a monitor. It consisted of two 5-volt voltage regulators,
and it worked. not having an ac source for the drives limited its usefulness, though.
CPU: 6502...........SPEED: 1.79 MHZ..............OS: ROM- RESIDENT
UP TO 4 5.25 INCH EXTERNAL, APPROX. 160 K EACH AT SINGLE DENSITY
SCREEN MODES: 3 TEXT, 9 GRAPHICS. ALL COLOR.
AUDIO: 4 INDEPENDANT CHANNELS,
PROGRAMMABLE BY FREQUENCY, DISTORTION, DURATION, AND VOLUME
The 8 k eprom cartridge was an ideal mode for commercial programs.
it is safe from accidental erasure, loads instantly, and frees
disk space for data.
Besides the extremely useful Atari Basic, word processors, screen art
programs, games, assembly language compilers, and other programming
languages are available.
Unlike IBM's MS (or PC) Dos, the various versions of atari dos are small programs dealing only with disk drive i/o and is needed only on boot disks. it presents a menu of disk and
file operations. by naming any executable binary file "autorun.sys", the dos menu
could be skipped and the chosen program run at bootup.
The rest of the o/s was rom-resident. It made booting MUCH faster.
Why didn't IBM think of that?
i/o to peripherals by a unique serial bus port, daisy chainable.
Each peripheral responds to its own unique command code, avoiding confusion
An rs-232 converter was available for non-atari modems and printers.
The serial connector used a proprietary 13-pin delta plug, hard to find elsewhere.
PINOUT: (2) (4) (6) (8) (10) (12)
(1) (3) (5) (7) (9) (11) (13)
1 clock in 5 data out 9 proceed 13 interrupt
2 clock out 6 ground 10 +5v ready
3 data in 7 command 11 audio in
4 ground 8 motor ctrl 12 nc
Motor contol started and stopped the cassette, and AUDIO IN fed the sound track
of the cassette to the tv sound output. Data used only one of the stereo tracks,
leaving the other for optional programmed pre-recorded sound.
JOYSTICK PORTS can be programmed for output, allowing remote control
via relays of any external device, or parallel intercomputer data transfer.
2 "paddles" per port can be connected, reading variable resistance.
Thermistors may be input also to read external temperature.
Light pens and external keypads are also read through these ports.
800 XL added a parallel interface port, but its use was not extensively developed.
JOYSTICK PORT PINOUTS:
(1) (2) (3) (4) (5)
(6) (7) (8) (9)
1=STICK FORWARD 2=STICK BACK 3=STICK LEFT 4=STICK RIGHT
5=POTENTIOMETER B 6=TRIGGER BUTTON 7=+5 VOLTS @50 MA
8=GROUND 9=POTENTIOMETER A
PADDLES ARE VARIABLE RESISTORS WITH A 1-MEGAOHM MAXIMUM.
READOUT IS AN INTEGER BETWEEN 0-228. EACH UNIT IS THE EQUIVALENT
OF 4.386 K-OHM.
EACH PORT COULD INPUT 5 BITS AND OUTPUT 4. USING TWO PORTS YOU
CAN HAVE AN 8-BIT PARALLEL INTERFACE. THE DATA IS READ OR WRITTEN
ON MEMORY LOCATION 54016. 54018 CONTROLS THE DIRECTION:
100 POKE 54018,48:POKE 54016,255:POKE 54018,52:REM SWITCH TO OUTPUT
110 POKE 54016,D:REM SEND DATA BYTE D
200 POKE 54018,48:POKE 54016,0:POKE 54018,52:REM SWITCH TO INPUT
210 DN=PEEK(54016):REM GET INCOMING DATA BYTE DN
EACH PORT CAN CONTROL 4 5-VOLT RELAYS AND READ 5 SENSOR SWITCHES
AND TWO RESISTANCE VALUES, MAKING IT EXCELLENT FOR ROBOTICS.
PARALLEL BUS (600XL, 800XL):
50-PIN CARD-EDGE CONNECTOR: TOP ROW--1-49 ODD #'S.
BOTTOM ROW-- 2-50 EVEN #'S
DATA: #7=most significant bit ~~~~~16 bit address: #15=msb
o-2=phase2 clock: high=data ok~~~~~low=transition phase
clock speed=1.8 mhz~~550 nanoseconds/cycle~~low for 300 ns~~~ high for 250 ns
read/write: high=reading low=writing
ATARI PARALLEL PINOUT
|1 ? ||2 ground ||3 address 1 ||4 address 0||5 address 3 |
|6 address 2 || 7 address 5|| 8 address 4 || 9 ground ||10 address 6|
| 11 address 8|| 12 address 7 || 13 address 10|| 14 address 9||15 address 12|
|16 address 11 ||17 address 14|| 18 address 13|| 19 address 15||20 ground|
| 21 data 1|| 22 data 0|| 23 data 3|| 24 data 2|| 25 data 5|
| 26 data 4|| 27 data 7 || 28 data 6|| 29 ground|| 30 ground|
| 31 ground || 32 phase 2 clock ||33 reset || 34 n/c || 35 ready|
| 36 irq || 37 ? || 38 n/c || 39 ? ||40 n/c|
|41 ground||42 n/c || 43 ras || 44 ? || 45 read/write |
| 46 ground|| 47 +5volts||48 +5volts||49 ground||50 ?|
besides the 6502 cpu (later the 6502c), the atari had 3 subordinate but powerful microprocessors.
CTIA or GTIA (color (or George's) tv interface adapter). ANTIC
controls most of GTIA's operations, but the 6502 can be programmed to
control it directly. GTIA converts the digital commands from ANTIC (or the 6502)
into the signal that goes to the tv or monitor. GTIA adds color values,
player-missle graphics, and collision detection.
george's chip replaced the ctia, adding improved color and graphic modes
POKEY (pot/keyboard, not slow) is a digital i/o chip. It handles the serial I/O bus, audio generation, keyboard scan, random number
generation, digitizes the resistive paddle inputs and controls maskable
interrupt (IRQ) requests from peripherals.
(alpha-numeric tv interface chip) antic gets the display list from RAM using direct memory access (DMA). it translates these instructions and sends them
to GTIA. it also controls system timers and input devices. it can be turned off with a poke during processing that doesn't require video or input,
to allow the 6502 to run faster without ANTIC's interrupts.
ANTIC OFF: POKE 590,0~~~~~~~ANTIC BACK ON: POKE 590,34
ATARI'S VERSION OF ASCII has a few differences. it uses all 256 codes. in display, 128-255 are negative images of 0-127 (print and background colors reversed).
a set of graphics characters was included to facilitate animated graphic displays in text modes, which is faster and uses less RAM than the graphics modes. you can also redifine as many characters as you wish, turn them upside down (poke 755,4), display control characters (poke 766,[>0]).
As time goes by I may add more of the considerable amount of information
I have on 8-bit atari hardware and programming. those who are already
atari fans and collectors may find nothing new, but those who have or
might acquire an orphaned atari, perhaps without peripherals,
might wonder how to get it up and running and discover some
of its unique features.
Atari enthusiasts have devised ways of interfacing ataris to ibm pc's,
adding more memory and hard drives, writing to atari-format disks with a pc,
and even accessing the internet.
MOST OF US FELT FROM THE BEGINNING THAT SOFTWARE SHOULD
BE FREE, SO DISK DRIVES AND MODIFICATIONS WERE DEVISED TO
DEFEAT COPY-PROTECTION SCHEMES, ENABLING BACK-UP COPIES
OF THE VULNERABLE FLOPPIES, AND SHARING AMONG FRIENDS
The newsgroup and the website links listed below are excellent sources for info
on modifications and innovations
The following magazines contained many program listings, both basic and
machine language, that can be typed in and saved:
analog computing, compute, and antic
check your library.
questions? email me.
(This link needs a configured newsreader:Outlook Express will work)
atari 8-bit faq
atari vendors faq
atari planet--holyoak com
FREE ATARI CATALOGS
BRAVO SIERRA'S DOWNLOADABLE/ON-LINE CATALOGS, POLICY and LINKS
Atari Computer Enthusiasts of Columbus
Phillipe's Atari Pages
Atari Historical Museum