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Transfer Points - Build Your Null Modem Adaptor for Moving Files Between



by Dan Keen and Robert Murray

Published June 1986

80 Micro, CW Communications/Peterborough Inc.


Many owners of Tandy MS-DOS computers face the Job of transferring Model I/III/4 files to their new machines.

transfer methods require extra hardware or software that can cost serious money. But for a few dollars, we built a

null modem device, which allowed us to move files from a Mode1 4 to a Tandy 1000 via their serial ports (see the

Photo]. Since TRS-DOS 6 has a COMM utility and the 1000 comes wish DeskMate, we didn't need additional

communications software. You could, of course, use a similar setup to move files between any two computers.


Making the Connection

To port files, your Tandy 1000 must have the RS-232C upgrade sold by

Radio Shack (stock number 25-1006, $99).


The Null modem is an adapter that you connect to one of the

computers, it crosses send and receive lines so the two machines

communicate. To build your own, you'll need male and female 25-pin

D-subminiature connectors (part numbers 276-1547 and 276-1548

respectively] or the equivalent. The Table shows the wiring

configuration. We tied pins 6, 8, and 20 together and the device still



Only nine pins have to be wired on each connector. Don't use ribbon

cable which is awkward for crossing connections. Use solid wire

instead of stranded for better support. The wire path should be flexible

the connectors won't dislodge if the computers are accidentally bumped. Figure 1 and Figure 2 show the protocols

you should use to configure DeskMate and SETCOM. Pressing the clear and 8 keys together gives you a menu

shoaling the COMM settings.









(c) 2004, 2005, Brian K. Hahn

 All Rights Reserved.