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The forgotten IBM PS/1 Audio Card (with IBM PCjr / Tandy 1000 sound)

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    #31
    Originally posted by theruler View Post
    Thanks, claudshatze, I totally missed that post.

    An user spoke of an home-made OPL3 based sound card connected to the proprietary IBM ps/1 bus. Are there schematics around? I would really enjoy making such a piece of hardware for my PS/1!
    I don't think he provided schematics. The IBM PS/1's game/audio connector has all the signals of an ISA slot you need except one, it does not have an OSC signal. You have to find that elsewhere on the board or you can build a clock circuit.
    My Retro Computing and Vintage Gaming Blog : http://nerdlypleasures.blogspot.com/

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      #32
      Quick question -- does the PS/1 midi sit at port 0x330 and behave as a dumb UART, or is it a non-standard address with proprietary programming? Will it work in Intelligent mode?

      I can't find any real information to confirm that one way or the other.

      If it is custom, I'd love to have the info to try and add it to my ever growing library of supported sound cards.
      From time to time the accessibility of a website must be refreshed with the blood of owners and designers. It is its natural manure.
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        #33
        The file ftp://ftp.oldskool.org/pub/IBM_PC_BBS/ps1/instdrv.exe contains MT32IBM.DRV which is a PS/1 MIDI-only driver for many Sierra games; a quick disassembly shows it writing to ports 330h, 333h, and 334h, and I didn't see any IRETs, so I'm assuming it is a dumb UART as you suspected. I've attached the quick'n'dirty disassembly.
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          #34
          Originally posted by Trixter View Post
          a quick disassembly shows it writing to ports 330h, 333h, and 334h, and I didn't see any IRETs, so I'm assuming it is a dumb UART as you suspected. I've attached the quick'n'dirty disassembly.
          The lack of read for response on 0x331 likely means it's not dumb UART though... or at least doesn't follow the MPU-401 standard even if it is sitting at the correct ports. The accesses to 0x333 and 0x334 are pretty non-standard in fact.

          MPU 401 Dumb UART mode only uses the base address and base + 1. (0x330 and 0x331 for normal config). Data port and status port respectively.

          It looks like it's reading 0x335 for status before write which is... strange. I'll have to dig into this a bit deeper.

          Hopefully I'll have better luck making sense of it than I did the IMF, but it's IBM so...
          From time to time the accessibility of a website must be refreshed with the blood of owners and designers. It is its natural manure.
          CUTCODEDOWN.COM

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            #35
            Originally posted by deathshadow View Post
            The lack of read for response on 0x331 likely means it's not dumb UART though... or at least doesn't follow the MPU-401 standard even if it is sitting at the correct ports. The accesses to 0x333 and 0x334 are pretty non-standard in fact.

            MPU 401 Dumb UART mode only uses the base address and base + 1. (0x330 and 0x331 for normal config). Data port and status port respectively.

            It looks like it's reading 0x335 for status before write which is... strange. I'll have to dig into this a bit deeper.
            This thread is long dead, but I'm poking at this and can't help but update (I wanted to get PS/1 MIDI supported in DoxBox or another emulator).

            From what I found, it's a UART, but not MPU-401 compatible. There's a scan of the technical manual that lists the registers (see p. A-8, A-13, A-22 to A-24):
            • 0x330 is the data port
            • 0x331 is interrupt enable (IRQ 7)
            • 0x332 is interrupt identification
            • 0x335 is status


            I've seen mentioned that the audio is very similar to Tandy, but I'm really just interested in the MIDI.

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