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Thread: Communication Multiplexer -- 68000 Conversion

  1. #1
    Join Date
    Jun 2018
    Pacific NW in the islands

    Default Communication Multiplexer -- 68000 Conversion

    Submitted for your approval, one Radio Shack Communication Multiplexer converted to a 68000 system....

    An interesting morning... This is the first time in 30 years that I've opened the top of this unit and looked in. Several of these systems were built at RS in various departments. We had two in Technical Support and I believe trsvax was built in a multiplexer too. There may have been some others. The benefit was the expanded card cage that allowed some, uh, customizations such as increased memory, several multi-terminal cards, and so forth. The massive linear power supply loafed along.

    I built this one and Valerie built the other, which we don't have. Looks like some cards were scavenged before I bought the unit which is not surprising. We did run a MMU in this machine, but it's not in the unit--I may still have one in a box of cards I haven't located yet. Looking at the front of the cage, the multi-terminal ribbon cables come in on the upper right with the normal ribbon cables feeding around the left side. You'll notice that the cage is color coded and this was to prevent the modem cards being installed incorrectly when this was used for it's original intent. The cage works backwards from the normal Model II/16 units--here it's Z80 boards on the left and 68K on the right side. The multi-terminal cards fed RS-232 concentrators that used intelligent switching so that we could multiplex more users into the machine then there were actual terminals. Many of the early Technical Bulletins were written using this unit, qat, as all of the tech-reps did their word processing on it. SCO Lyrix was the word processing software and the machine offered a curses based windowing system allowing multiple textual windows on the same screen each running different processes. It's uucp address was ...!ihnp4!trsvax!qat .

    It's pretty dirty, but nothing dead is laying around inside. The plenum foam is bad and needs replacing, needs a good cleaning and the power supply will get my first attention when I get around to working on it. In the two large boxes there's the console unit for this system with 2 drives. The other box holds a Beehive terminal in which I replaced the dead main board with a ZRT-80 terminal board kit. Very whizzy at the time.

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  2. #2


    Wow, it's fascinating to finally see one of these in detail. One of the rarest Tandy peripherals/computers for certain! Thanks for sharing.


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