len@qumix.UUCP (Leonard Labar) (11/26/84)
Subject: Commodore to Mac Null modem cable
The first chart below works for connecting a Mac to a Vicmodem. The
second chart is a null modem cable for connecting a Mac to a Vic20 or
C64. I just got it working. What this does is (1) saves me $471 since
I already have a dot matrix printer connected to my Vic (2) saves me
$1600 since I can use the Vic to debug Mac SW without buying a 2nd Mac.
-----RS422 (+5 volts line driver/receiver)------
MAC function breadboard VICMODEM function
(conn. 1)
1 ground ground 1, A ground
2 +5v pwr to ic -----
4 TXD+ --> 3.3k pullup --> M data to modem
5 TXD- ---- ----
6 filtered +12v ---- 10 modem power
7 carrier detect<- LS04-6 5 to <- H carrier detect
8 RXD+ ---- -----
9 RXD- <-- LS04-4 &1k res., 3 to <-- C data from modem
back of mac
-------------
\ 5 4 3 2 1 /
\ 9 8 7 6 /
--------
Null modem cable:
conn. 1 signal conn. 2 (to CBM)
1,A GND 1,A
M TXD --> B,C (RXD)
C <-- RXD M (TXD)
H to GND carrier detect H to GND
So now I can type on the CBM keyboard and everything appears on the Mac