Foreword
I own at least one of all the computers shown on this website. But I don't own any Atari DS800.
What is the Atari DS800 computer?
The DS800 is an Atari 800 Personal Computer System internally modified to support cartridge program development. Changes made are primarily to support a particular 6502 program development monitor called "LNBUG".
LNBUG works with a separate terminal for monitor communications, and a host computer for program editing, assembly, and downloading object code.
The DS800 also provides a processor bus port for either a logic analyzer, or an external memory mapped peripheral device (such as a floppy disc drive controller).
A computer or just an extra side board?
The main feature of the DS800 is the addition of a DS800 side board in a classic Atari 800, providing additional connectors, that's obvious. But it's more than that. A new DS800 CPU board also remplaces the standard production 800 CPU board. This specific DS800 CPU board includes data buffers, miscellaneous logic, and a 40-pin flat cable connector. The standard 9V AC power supply is inadequate to power the additional circuitry, so a higher current unit is also required.
As a result, DS800 is not simply the name of a side board, but the name of the model modified for cartridge development: an Atari DS800.
Demonstrated by the late Curt Vendel
In this fantastic video posted by DrGuillotine and taking place during the Vintage Computer Festival East 2019 (VCFEAST 2019), Curt shows off some rare hardware, including this DS800.
The name of the computer is not correctly identified, but this is not important.
Availability
Two LNBUG software manuals have been discovered, dating respectively from December 1979 (LNBUG version 6.0) and 1981 (no details of the month, LNBUG version not identified). Since the LNBUG software requires an Atari DS800 to run, we can assume that this DS800 model was available at least between 1979 and 1981.
There is every reason to believe that this DS800 was only available internally, at Atari, to the teams responsible for developing the cartridges. No information is available on whether it was made available to external companies — I seriously doubt it. This model was obviously not sold.
What are the differences between the Atari DS800 and the standard Atari 800 computer?
Externally, the DS800 features:
- A visible side panel on the left side, equipped with additional connectors.
- A different power supply, necessary to accommodate the increased power consumption.
Internally, the DS800 features:
- A DS800 side board.
- A DS800 CPU board.
- Additional cables.
Programmer's workstation
A complete programmer's workstation would include:
- An Atari DS800
- Monitor terminal, such as ADM-31
- Host computer hookup, via direct line or modem
- Television set
- Any Atari Personal Computer System peripherals and/or controllers
- A logic analyzer, such as an HP 1611A2
A minimum workstation, which a programmer might take home, could include:
- An Atari DS800
- Terminal with a built-in modem, such as a TI-7453
- Television set
- Atari Personal Computer System peripherals and/or controllers
Side panel
There are two 9-pin "D" connectors on the left side panel. These are electrically and mechanically compatible with the RS-232-C ports found on the Atari 850 Interface Module. The left one (as viewed from the front side) is for communication with a host computer. The right one is for use with the local terminal.
The address, data and control buses of the ATARI 800 are brought out to a 40-pin flat cable connector on the left side panel. The signals are arranged so that a Hewlett-Packard 1611A logic analyzer can be plugged in for tracing processor activity.
A gated clock is provided so that ANTIC DMA signal and an ungated clock are also provided, so that the ANTIC itself can be traced.
An "External Select" input is provided, for attaching external memory mapped devices.
At the right side of the panel is a double momentary reset switch. It controls the two major states of the DS800, "Internal" mode, and "External" mode.
In "External mode, a reset is vectored through location $7FFC, and all memory mapped devices on the side board are enabled;
in "Internal" mode, a reset is vectored through location $FFFC, and all side board memory devices are disabled.
CPU board theory of operation
The DS800 CPU board was designed with three goals in mind:
- Standalone compatibility with production CPU board.
- NTSC/PAL compatibility.
- Add as little logic as possible for compatibility with external LNBUG hardware.
The logic on the CPU board is based on the PAL version, which is inherently NTSC/PAL compatible by swapping the ANTIC and GTIA.
Four ICs were added to crowded DS800 CPU board:
- A second 74LS244 address bus buffer was added, to compensate for the cable and side board capacitive loads.
- A 74LS245 data bus buffer was added, both for loading considerations, and to allow external memory devices to be superimposed in the ATARI 800 address space.
- 74LS00 and 74LS02 gates were added for:
- Control Data Bus Buffer
- Gate R/W for write protection
- Gate NMI for single stepping
- Derive a PH2 gated by DMA, so that a Logic Analyzer can distinguish processor cycles from ANTIC cycles.
- Buffer the clock into the PAL oscillator
More information
The "Atari DS800/LNBUG User's guide" document available in the "Rare Atari Documents" section will give you all the details.
Special thanks to Dutchman2000 & Atarimania.