# C64 RS232 User Port

Available on the Commodore C64/C128. Software emulated. The signals does not have true RS232 levels. It's TTL level, and RXD/TXD is inverted. It's just the normal User Port, used as a RS232 port.

(at the computer)

UNKNOWN CONNECTOR at the computer.

Pin | Name | RS232 | Description
--- | --- | --- | ---
A | GND | GND | Protective Ground
B+C | FLAG2+PB0 | RxD | Receive Data (Must be applied to both pins!)
D | PB1 | RTS | Ready To Send
E | PB2 | DTR | Data Terminal Ready
F | PB3 | RI | Ring Indicator
H | PB4 | DCD | Data Carrier Detect
K | PB6 | CTS | Clear To Send
L | PB7 | DSR | Data Set Ready
M | PA2 | TxD | Transmit Data
N | GND | GND | Signal Ground

Contributor: Joakim Ögren, Arwin Vosselman, Mark Sokos

Source:
Usenet posting in comp.sys.cbm - Help on modem -> c64 by Lasher Glenn
Commodore 64 Programmer's Reference Guide

Copyright © The Hardware Book Team 1996-2001.
May be copied and redistributed, partially or in whole, as appropriate.
Document last modified: 2001-06-08