Atari 850
| Atari 850 Interface Module | |
|---|---|
 |
|
| Atari 850 in the beige plastic case | |
| Manufacturer | Atari, Inc. |
| Type | Serial and parallel interface module |
| Release date | Introduced January 1980; shipping from about autumn 1980[1] |
| Price | US$219.95 (announced 1980)[1] |
| Interface | Atari SIO, two 13-pin I/O connectors; four 9-pin RS-232-C serial ports; one 15-pin parallel printer port[1] |
| Compatible | Atari 400, Atari 800 and later Atari 8-bit computers[1] |
| Power | External 9 V AC adaptor; 17 W[1] |
The Atari 850 Interface Module connects an Atari 8-bit computer to standard RS-232-C serial devices and to a Centronics-type parallel printer. It plugs into the computer's serial I/O (SIO) bus and has four serial ports and one parallel port.[2] Atari's own Atari 825 printer and Atari 830 acoustic modem both need it.[3] Atari introduced the 850, the 825 and the 830 at the Winter Consumer Electronics Show in January 1980 and shipped them in about the autumn of that year.[1]
Hardware
[edit | edit source]The 850 is built around a 6507 processor running a 4 KB ROM that holds its operating firmware and the R: device handler. Two 6532 chips provide the I/O lines, a programmable timer each and 128 bytes of RAM each, so the module has 256 bytes of local RAM as a data buffer. Buffers isolate these chips from the ports: LM349 op amps (A105, A106) and CA3086 transistor arrays (A107, A108) on the serial ports, and two more CA3086 arrays (A110, A111) on the printer port.[2]
| Position | Device | Atari part number |
|---|---|---|
| A101 | 6507 processor | C010745 |
| A102 | ROM, 4K × 8 | C012099 |
| A103, A104 | 6532 RAM-I/O-timer | C010750 |
| A105, A106 | LM349 op amp | C015769 |
| A107, A108, A110, A111 | CA3086 transistor array | C010174 |
| A109 | High-beta transistor array | C016821 |
| A112 | +5 V regulator on heatsink | CA016075 |
| A113 | 7805 regulator, used for +10 V | C014348 |
| X101 | 4.433618 MHz crystal | C012284 |
The crystal is divided by four to give a 1.1084045 MHz clock for the 6507.[2] The board makes its own +5 V, +10 V and -8 V from the 9 V AC adaptor; the +10 V and -8 V rails feed only the serial port line drivers and, for +10 V, the clock circuit.[2] The ROM part number ends in its software revision, so a ROM stamped C012099-03 holds revision 3; it can be read through a sliding window in the RF shield.[2]
Early units have a black anodised aluminium case and most have a beige plastic case matching the 400 and 800.[1][2]
Ports
[edit | edit source]| Port | Connector | Signals |
|---|---|---|
| Serial 1 | 9-pin socket | Send and receive data, DTR, RTS, DSR, CTS, carrier detect |
| Serial 2 and 3 | 9-pin socket | Send and receive data, DTR, DSR |
| Serial 4 | 9-pin socket | Send and receive data; +10 V and -8 V for a 20 mA current loop such as a teletype |
| Parallel | 15-pin socket | Eight data bits, data strobe, busy, fault; pin 9 is a +5 V pull-up |
Supported serial speeds run from 45.5 to 9,600 bit/s.[1] The ports use Atari's own pinouts, so standard devices need Atari's cables or equivalents: the CX86 printer cable (supplied with the 825), the CX87 modem cable (supplied with the 830) and the CX88 terminal cable.[1] The parallel port works only while the printer holds the FAULT line (pin 12) high.[2]
Booting and the R: handler
[edit | edit source]The computer's operating system has no handler for the serial ports, so the 850 supplies one from its ROM. At switch-on the computer asks disk drive 1 for its status. If no drive 1 answers, the 850 answers in its place and the computer loads the handler from it as if booting a disk. If a drive 1 is present, DOS must load the handler, which DOS 2.0S and later versions can do.[1][2] For this reason the 850 must be switched on before the computer; otherwise a program trying to use it gets an error, usually ERROR 138, or "RS 232 ERROR: 130".[3] The parallel port needs no handler, because the operating system's P: device drives it.[1]
Known faults
[edit | edit source]Atari's service manual sorts faults by whether the module still boots:[2]
- Serial errors on all ports, or a port that works with some devices and not others, point to the +10 V or -8 V supply. A hot +10 V regulator (A113) with low output points to a line driver (A105 or A106) loading the rail.
- Errors on one port point to its buffers, A105 to A108.
- If the printer prints during the boot, the local RAM test has failed (A103 or A104).
- Printer garbling or dropped bits point to the printer port buffers A110 and A111, then A103.
- A module that does not boot is checked in this order: +5 V, clock, power-on reset, 6507, ROM, local RAM and the system I/O buffers. A loose heatsink on A112 lets the regulator overheat.
The Atari 850 Troubleshooting guide gives the test points and voltages, the Atari 850 Maintenance Guide covers cleaning, inspection and the port test, and the Atari 850 Capacitor Replacement Guide lists the electrolytics.
Documentation
[edit | edit source]- Atari 850 Documentation: the service manual, operator's manual and technical manual, with contents and notes.
- 850 Interface Module Service Manual (CS 400/800-S004-B, 1981)
- Atari 850 Interface Module Operator's Manual (C017651, 1982)
- Atari 850 Interface Module Technical Manual (C017652 Rev. B, 1982)
Gallery
[edit | edit source]-
Board with power supply test points (service manual figure A3-2) -
Power supply schematic (service manual figure A3-1)
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Related pages
[edit | edit source]- Atari 850 Maintenance Guide
- Atari 850 Troubleshooting
- Atari 850 Capacitor Replacement Guide
- Atari 850 Documentation
- Atari 830
- Atari 825
References
[edit | edit source]- ↑ 1.00 1.01 1.02 1.03 1.04 1.05 1.06 1.07 1.08 1.09 1.10 Michael D. Current (ed.), Atari 8-Bit Computers: Frequently Asked Questions, comp.sys.atari.8bit FAQ, last modified 2 August 2026: section 5.2.1 (the Atari 850 Interface Module) and section 11.1 (history, 1980). mcurrent.name. Community reference.
- ↑ 2.0 2.1 2.2 2.3 2.4 2.5 2.6 2.7 2.8 Atari, Inc., 850 Interface Module Service Manual (CS 400/800-S004-B, April 1981): description and installation pp. 1-2 to 1-4; principles of operation pp. 2-3 to 2-8; maintenance and troubleshooting pp. 3-2 to 3-18; power supply, appendix 3; clock circuit, appendix 4; revision level, appendix 6; parts list, appendix 8. Hosted here as File:Atari 850 Interface Module Service Manual CS400-800-S004-B.pdf.
- ↑ 3.0 3.1 Atari, Inc., Atari 850 Interface Module Operator's Manual (C017651, 1982): introduction, system requirements, installation, use and troubleshooting. Hosted here as File:Atari 850 Interface Module Operator's Manual C017651.pdf.