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MFJ-1278B MULTI-MODE COMPUTER INTERFACING
Commodore C64, C128 and VIC-20
The MFJ-1278B has a built-in TTL-level port for interfacing with the Commodore C64,
C128 or the VIC-20 computers. You do not need a RS-232C converter to interface with the
MFJ-1278B.
An optional Starter Pack for the C-64, C-128 or the VIC-20 is available from MFJ
Enterprises, Inc. or any dealer of MFJ products. The Starter Pack includes a cable from the
MFJ-1278B TTL port to the user I/O port on the Commodore computer. Included also is a
terminal program. To order, specify MFJ-1282B for software on disk or MFJ-1283 for
software on tape. If you wish to construct your own cable, the information below in Figure 2-
2A will be helpful:
MFJ-1278B
J-5,Pin#
Mnemonic
Name
C-64/128*, VIC-20 Pin#
1 RXD Receive Data B,C
2 DCD Data Carrier Detected H
3 GND Ground (Frame and Signal) N
4 RTS Ready To Send E**
5 TXD Transmit Data M
6 DSR Data Set Ready L
7 CTS Clear to Send K
Fig. 2-2A TTL Port wiring for VIC-20, C64 and C128
*C-128 is used in the C-64 mode for these connections.
**Pin E is not needed when using terminal program referred to in this chapter for the
Commodore computers.
The TTL port (J5), is numbered from left to right as viewed from the back panel of the MFJ-
1278B. The user's terminal program may not use all of these connections. The MFJ-1278B
requires RXD, TXD and GND connected for proper operation. Programs that utilize file
transfer and printer routines will probably use RTS and CTS as well. Consult your software
documentation.
IBM PCjr
The PCjr uses standard serial voltage levels for it's RS-232C interface; however, the
connector used is non-standard and not readily available from electronic supply dealers. The
pin-out information for this connector is refered to in the IBM PCjr Technical Reference
Manual.
IBM dealers sell an "IBM PCjr Adapter Cable for Serial Devices". This Adapter Cable is