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Thread: Tandy Sound Compatible PCB

  1. #11
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    By the way, the idea was also discussed on the Vogons forum a while ago. Perhaps there's some useful information in this thread: http://www.vogons.org/viewtopic.php?f=46&t=42521

  2. #12

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    Add a MIDI port and you could also make it compatible with the IBM PS/1 Audio Card.

    http://www.vcfed.org/forum/showthread.php?38915

  3. #13
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    Interestingly, to get from C0 to 1E0 only requires flipping two of the address bits :

    C0 = 00 1100 0000
    1E0 = 01 1110 0000


    I would also be happy to try it at both addresses in my 5160.

    The issue with 2C0 is no software uses that address, every Tandy-supporting program would need to be modified to direct its data to that port. Alternatively, a SoftMPU virtual 8086 mode (386+) port trapping driver would be needed to divert the writes.

    A nice idea to allow for PC Speaker input and output. Any ideas about a bracket for this card, or is it a "drill or 3-D print your own"?
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  4. #14
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    Quote Originally Posted by Great Hierophant View Post
    The issue with 2C0 is no software uses that address, every Tandy-supporting program would need to be modified to direct its data to that port.
    Yes, but wouldn't the majority of software be hardcoded to C0 anyway, seeing as most PCjr/Tandy titles predate the machines that put the chip at 1E0?
    So you'd need to patch existing software anyway. Whether you patch it from C0 to 1E0 or 2C0 doesn't matter then.
    Patching shouldn't be too difficult, I would think. With DOSBox it should be quite simple to intercept writes to C0-C7 and pin-point the music routine in any game almost instantly.

  5. #15
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    Obviously without schematics we can't be sure how address decode is done, but perhaps consider using DIP switches or shunt headers for one input to a comparator like the 74xx688. It's a tiny board so you've got plenty of room to make it larger within even the Slot 8 constraints of an ISA card.

  6. #16
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    James is almost certainly using a 74*688 for IC1 (addressing), a 74*74 for IC2 (clock division), the SN76489 is at IC3 and IC4 is a LM386 amplifier.
    Last edited by Great Hierophant; November 1st, 2016 at 07:17 PM.
    My Retro Computing and Vintage Gaming Blog : http://nerdlypleasures.blogspot.com/

  7. #17

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    Thanks for all the input on this.

    Re bracket - it has the same hole placement as the ISA-USB adapter. Someone kindly provided a CAD file suitable for laser cutting, which I need to dig out and make available. Or of course 3D print in e.g. phosphor bronze works pretty well (at a price).

    I've updated the image (ctrl-r on the 1st page to see it). Three address options provided as suggested also the silk change. The audio amp has some refinements too.

    Can anyone suggest an audio taper pot preset? I can only find linear.

    Incidentally note that this is synth only - no DAC. So no Deskmate sampled audio.

  8. #18
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    Quote Originally Posted by pearce_jj View Post
    Re bracket - it has the same hole placement as the ISA-USB adapter. Someone kindly provided a CAD file suitable for laser cutting, which I need to dig out and make available. Or of course 3D print in e.g. phosphor bronze works pretty well (at a price).
    Not my project but still, why aren't you using a standard Keystone bracket? They're cheap and available. You can place a tab on the PC board to accommodate it or just make the board larger. A larger board *has* to be cheaper than 3D printing, probably even in PLA or ABS, but definitely vs. bronze! I could see the laser cutting method being cheaper if you're ordering a big pile, or if you happen to have a laser cutter at home/work/your hackerspace.

  9. #19

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    How about 0x0205 for PS/1 compatibility? They used that range to avoid the conflicts. It's functionally identical on the PS/1 apart from sitting at that address -- they put it in the game port reserved space since who reads anything other than 0x0201?
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  10. #20
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    Quote Originally Posted by deathshadow View Post
    How about 0x0205 for PS/1 compatibility? They used that range to avoid the conflicts. It's functionally identical on the PS/1 apart from sitting at that address -- they put it in the game port reserved space since who reads anything other than 0x0201?
    With the PS/1 you also bring in the detection issues, the lack of a DAC and the slightly weird gameport. All games but one that support the PS/1 support the Tandy and far many more support the Tandy than the PS/1.
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