# Mac to C64 Nullmodem

The RS-232 standard on the C64 is a little bit strange. It uses inverted TTL level for the signals. The RS-422 ports on the Macintosh has both an inverted and non-inverted input. By using the inverted instead of non-inverted the inverted C64 level is back to normal.

(at the Computer)
(to the C64).

8 PIN MINI-DIN MALE to the Macintosh.
DZM 12 DREH to the C64 UserPort.

| Mac | C64 |
--- | --- | --- | ---
GND+RXD- | 4+5 | 1+12+A+N | GND
RXD+ | 8 | M | TXD (PA2)
TXD+ | 6 | B+C | RXD (FLAG2+PB0)
|  | D+E | RTS+DTR (PB1+PB2)

Note: Larry Anderson suggested that RXD- should not be connected. However earlier information indicated that it should be connected. Please inform us if the above connection is sufficient.

GND+RXD- | 4+5 | 1+12+A+N | GND

Contributor: | Joakim Ögren, Pierre Olivier, Larry Anderson

Source: | Usenet posting in comp.sys.cbm, A very simple C64 to Macintosh serial cable by Chris Baird

Copyright © The Hardware Book Team 1996-2004.
May be copied and redistributed, partially or in whole, as appropriate.
Document last modified: 2002-01-13