Atari 8-Bit Computer
850 Interface Module
Serial Ports
The 850 Interface has 4 serial ports on the back. When facing the back the serial ports are labeled 4 to 1 from left to right.
 |  |
 |  |
| Pin | Description | |||
|---|---|---|---|---|
| Port 1 | Port 2 | Port 3 | Port 4 | |
| 1 | Data Terminal Ready (DTR, Ready Out) | |||
| 2 | Carrier Detect (CRX, In) | Not Connected | ||
| 3 | Send Data (Out) | |||
| 4 | Receive Data (In) | |||
| 5 | Signal Ground | |||
| 6 | Data Set Ready (DSR, Ready In) | Not Connected | ||
| 7 | Request to Send (RTS, Out) | Not Connected | Request to Send (RTS, Out) | |
| 8 | Clear to Send (CTS, In) | Not Connected | ||
| 9 | Not Connected | -8V | ||
Pins 1 and 7 on port 4 are not computer-controlled and are always ON (+10V).