6.1) What is the Atari 850 Interface Module?

Subject: 6.1) What is the Atari 850 Interface Module?

While the Atari's SIO and controller ports did not conform to established
industry standards, Atari produced the 850 Interface Module to address this
issue. The 850 connects to the SIO port on the Atari, and provides:

- four 9-pin serial EIA RS232C ports
- One 15-pin 8-bit parallel Centronics-type port

Many "industry standard" (of the time) printers, modems, and various other
devices can be used with the Atari computer in combination with an 850
Interface Module.

Early 850's are in an all metal (black) case, but most are in a plastic beige
case matching the 400/800 computers. Other features:
- programmable baud rate on any port, including:
75, 110, 134.5, 150, 300, 600, 1200, 1800, 2400, 4800, and 9600 bps;
baudot speeds of 60, 66, 75, 100 words per minute
- uses standard ASCII. Baudot support for radio-teletype (RTTY).

(please see attachment for ascii-art pinouts in a readable txt file)

PINOUTS

850 R1: Serial port DB9P:
5 4 3 2 1 ____________________________
9 8 7 6 / DB25P
1. DTR - Data Terminal Ready (out) + 20
2. CRX - Signal (carrier) Detect (in) + 8
3. XMT - Transmitted Data (out) + 2
4. RCV - Received Data (in) + 3
5. GND - Signal Ground + 7
6. DSR - Data Set Ready (in) + 6
7. RTS - Request to Send (out) + 4
8. CTS - Clear to Send (in) + 5
No connection to shield + Frame - to the shield wire

850 R2: Serial port DB9P:
5 4 3 2 1
9 8 7 6
1. DTR
3. Send Data
4. Receive Data
5. Signal Ground
6. DSR

850 R3: Serial port DB9P:
5 4 3 2 1
9 8 7 6
1. DTR
3. Send Data
4. Receive
5. Signal Ground
7. RTS
8. -8 Volts

850 R4: Serial port DB9P:
5 4 3 2 1
9 8 7 6
1. Send Data +
3. Send Data -
7. Receive Data +
9. Receive Data - (20 mA)

850 P: Parallel port DB15P:
8 7 6 5 4 3 2 1 ____________________________
15 14 13 12 11 10 9 / 36 pin Centronics (male)
1. Data Strobe + 1
2. D0 + 2
3. D1 + 3
4. D2 + 4
5. D3 + 5
6. D4 + 6
7. D5 + 7
8. D6 + 8
9. Data Pull up (+5v) +
10. - +
11. Ground + 16
12. Fault + 32
13. Busy + 11
14. - +
15. D7 + 9
No connection to shield + Frame - to the shield wire

Because the 850 was relatively expensive, provided more capabilities than the
average user was looking for, and was at times unavailable from Atari despite
high demand, there were many 3rd-party interfaces designed to provide some
compatible subset of the 850's features. Perhaps the most prominent example
of such a product is the P:R: Connection from ICD.