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Thread: List of Standard TRS 80 IO Ports

  1. #1

    Default List of Standard TRS 80 IO Ports

    I am looking for a comprehensive list of the IO port numbers used by "standard" Model 1 (III, ...) hardware extensions (e.g., the SC100 Voice Synthesizer uses Port 11). How about hard drives etc.

    I want to build my own hardware extension and need to know which ports are "available" and don't clash with other hardware.

    Can someone point me to such a list please.

  2. #2
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    A problem is that I believe some devices (e.g. a popular joystick interface) assume they're the only device on the external bus and use lazy address decoding and respond to multiple (or all) external port addresses. This allowed them to use less chips for address decoding.

  3. #3
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    I've also heard the joysticks tended to use highly mirrored decoding. In my own disassembling I've seen joystick reads from ports $00, $13 and $F7. The last is right up there in the floppy disk area but the 4P technical reference manuals says it is available for reading. The Alpha joystick manual says to use port $00.

    $E0 .. $FF is the bulk of the standard hardware (cassette, floppy, printer, RS-232).
    $C0 .. $CF is the hard drive.
    $9C .. $9F is ROM switchout on Model 4P
    $90 .. $93 is the speaker on Model 4
    $80 .. $8F is for hires graphics

    Everything below $80 is the wild west.

    Radio Shack devices tending to allocate port ranges in blocks of 4; sometimes 2 or 4 blocks for a device.

    Orchestra 80 uses port $BD. Don't recall what port the stereo version uses.

    CHROMAtrs uses 8 ports, default $78 .. $7F but can be jumpered at any multiple of 8 from $00 .. $78.

    There were several Model I hires boards that were memory mapped with a bit or two added onto port $FF.

    The Exatron Stringy Floppy (and Aculab Floppy tape; same hardware) used port $F0 + N for drive N from 0 .. 7 though I doubt anybody had more than two. This conflicts with the floppy drive on Model 3 and 4 but not Model I as it is memory mapped.

    Alpha Products Newclock-80 uses $B0 .. $BC (according to their "PORTHELP" BASIC program)

    For modern day devices:

    FreHD stays within the standard hard-drive range ($C0 .. $CF). I believe that's generally true of any hard-drive emulator like the Lo-Tech IDE interface.

    MSIE mostly uses the ports of devices it emulates (e.g. Newclock-80). I see that it does use $F0 and $F1 for VGA colour control.
    Port $BE to control the joystick mode and other features. I don't know what ports it uses for the network or 256 byte EEPROM access.

    M3SE uses ports $70 .. $7D for VGA control. Emulates Newclock-80. Port $BE, $BF for feature control. Product information (read only) on ports $40 .. $43. I don't know what ports it uses for the network or 256 byte EEPROM access.

    TRSnic and TRSio I believe only use port $31.

    I think if your device could be set up with jumpers/DIP switches/flashed to be like the CHROMAtrs (i.e., base of $00, $08, $10, ... $70, $78 ) that would be quite acceptable. There are some ports available above $80 but I think it'd be just as well to stay away.

  4. #4

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    Quote Originally Posted by gp2000 View Post
    I think if your device could be set up with jumpers/DIP switches/flashed to be like the CHROMAtrs (i.e., base of $00, $08, $10, ... $70, $78 ) that would be quite acceptable. There are some ports available above $80 but I think it'd be just as well to stay away.
    Excellent list, thanks a lot for the great post!! A very good reference for anybody wanting to build something.

    Yes, DIP switches are a good idea.

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