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Thread: Inboard 386/PC 2mb expansion CLONE

  1. #1

    Default Inboard 386/PC 2mb expansion CLONE

    As there is a lot of demand for new 2 and 4 mb expansion boards for the Inboard 386/PC, I had originally begun to develop a clone of that card. I had lost interest a few months into development and left the further work on my PCB layouts alone.

    Harrison Frasier has contacted me a few weeks ago asking about info on my work. Since I was not able to invest more time into that project, I gave him all the PCB layouts and info I could find.

    Based on the data Harrison designed a new PCB prototype.
    He built and successfully tested the 2mb prototype a few days ago. There are still some uncertain thing to figure out but it's a big step forward.


    Further work and development:
    Harrison is now the owner and project manager of the expansion. I will get 2 bare prototype PCB from him to test different memory modules, TTL ICs and maybe add some modifications to get 4 or 8mb to work. My part is now to support and beta-test (which im happy with). Im glad that Harrison has taken the project up and got it to another milestone.

    I think we are very close

    This thread is meant as a central info point for the project.
    references:
    Seeking-memory-card-for-InBoard-386/page3

  2. #2

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    I have built one prototype with one of the PCB i was given by Harrison. It seems to work normally and has caused no problems so far. I have tinkered a bit with the not connected signal on pin 15 of the J2 connector. It is neither another RAS-enable line nor a CAS-enable line. We help from someone who owns a 4mb expansion for the inboard to measure the connections of pins 11-27 on the J2 connector.
    The white areas need to be verified on the 4Mb expansion.

    50597625068_4501221964_o.png

    The address-lines are inverted by two 74AS1004 (=7404) and routed to the corresponding address line on the RAM ICs. The address line 9 in the picture should be checked since it is not connected on the 2Mb card.
    The RAS and CAS signals should be generated by the two 74AS1032 ICs. The address lines from the 74'04 inverters and generated RAS/CAS signals from the 74'32 or-gates are routed to the RAM ICs through 22 Ohm resistors via resistor networks (4308R-102 220) on the 2Mb card (should be the same on the 4Mb card).

    50598542307_6c34a4a6c0_o.png

    My knowledge regarding 386 memory controllers is very limited (non-existent). I would really like to see a comment on this thread

    50597706633_9f7037262e_o.jpg

    Success with 4mb

    50597802458_5096574527_o.jpg

    -Jonas
    Last edited by stynx; November 13th, 2020 at 01:39 PM.

  3. #3

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    We have to test a bit more but i think that Harrison will be able to offer a 4Mb expansion in the near future

    -Jonas

  4. #4

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    Another working prototype (low effort) without resistors and capacitors. 4 Simms directly soldered to the card.
    PS2 modules would be nice but they will not work since the have bidirectional parity lines. The Inboards needs separate parity input and output lines. It may be possible to take a 74'244 and use the ^WE lines (seem to have identical signals) to separate the parity access between read and write. May be and interesting project
    50599838468_6bac247158_o.jpg
    -Jonas

  5. #5

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    I have desoldered the RAS-generator PAL (301094-001) from one of my defective Inboards and could read out its contents.
    the equations look like this:
    Code:
    PAL20L8B
    1: A22
    2: A21
    3: A20
    4: A19
    5: A18
    6: A17
    7: A16
    8: A23
    9: from PAL U75
    10: from PAL U76
    11:from PAL U74
    12 GND
    13:
    14:
    15: RAS to 4Mb Bank
    16:
    17:
    18:
    19:
    20:
    21: RAS0 to 1Mb Bank (1)
    22: RAS1 to 1Mb Bank (2)
    23:
    24 VCC
    
    
    Inputs:
    
    
    1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 13, 14, 16, 17, 18, 19, 20, 21, 23
    
    
    Outputs:
    
    
    15 (Combinatorial, No output feedback, Active low)
    17 (Combinatorial, Output feedback output, Active low)
    18 (Combinatorial, Output feedback output, Active low)
    19 (Combinatorial, Output feedback output, Active low)
    20 (Combinatorial, Output feedback output, Active low)
    21 (Combinatorial, Output feedback output, Active low)
    22 (Combinatorial, No output feedback, Active low)
    
    
    Equations:
    
    
    /o15 = (A22)& /(A21)& /(A19)& /(A18)& /(A23) & i9 & i16 +
           /(A22)& (A20)& (A18)& /(A23) & i9 & i16 & /i23 +
           /(A22)& (A20)& (A19)& /(A23) & i9 & i16 & /i23 +
           /(A22)& (A21)& /(A23) & i9 & i16 +
           (A22)& /(A21)& /(A20)& /(A23) & i9 & i16 +
           i11 & /i16
    o15.oe = vcc
    
    
    /o17 = (A22)& /(A18)+
           (A21)& /(A18)+
           /(A18)& i23 +
           /(A18)& (A17)+
           (A19)& /(A18)+
           /(A20)& /(A18)
    o17.oe = vcc
    
    
    /o18 = (A22)& /(A19)+
           /(A19)& i23 +
           /(A19)& (A18)+
           (A21)& /(A19)+
           /(A20)& /i4
    o18.oe = vcc
    
    
    /o19 = (A18)& (A17)& (A16)& /i10 & i13 & i14 +
           /(A18)& /(A17)& /(A23) & i13 +
           (A20)& /(A23) & i13 & /i23 +
           /(A19)& /(A23) & i13 +
           (A22)& /(A23) & i13 +
           (A23) & i13 & i14 +
           (A21)& /(A23) & i13
    o19.oe = vcc
    
    
    /o20 = (A22)& (A21)& (A20)& (A19)& (A18)& (A17)& (A16)& (A23) & i9 & /i10 & i14 +
           /(A22)& /(A21)& /(A19)& /(A18)& /(A23) & i9 +
           /(A22)& /(A21)& /(A23) & i9 & i23 +
           /(A22)& /(A21)& /(A20)& /(A23) & i9 +
           (A22)& /(A21)& (A20)& (A19)& /(A23) & i9 & /i14 +
           /i16
    o20.oe = vcc
    
    
    /o21 = i11 & /i16 +
           /(A22)& (A21)& /(A20)& /(A19)& /(A18)& /(A23) & i9 & i16 +
           /(A22)& /(A21)& (A20)& (A18)& /(A23) & i9 & i16 & /i23 +
           /(A22)& /(A21)& (A20)& (A19)& /(A23) & i9 & i16 & /i23
    o21.oe = vcc
    
    
    /o22 = i11 & /i16 +
           /(A22)& (A21)& (A20)& /(A19)& /(A18)& /(A23) & i9 & i16 +
           /(A22)& (A21)& /(A20)& (A18)& /(A23) & i9 & i16 +
           /(A22)& (A21)& /(A20)& (A19)& /(A23) & i9 & i16
    o22.oe = vcc
    this means:

    for the 4mb address space:
    0x14 0000 - 0x3F FFFF
    0x18 0000 - 0x38 FFFF
    0x20 0000 - 0x3F FFFF
    0x40 0000 - 0x4F FFFF
    0x40 0000 - 0x53 FFFF

    Resulting in 0x140000 - 0x53FFFF (4Mb with a 256k shift up)

    The two 1Mb banks of the 2Mb expansion are similar:
    0x140000 - 0x23FFFF for bank 1 and
    0x240000 - 0x3FFFF for bank 2

    To address more memory, we would have to swap out the RAS-generator PAL (301094-001) with a new modified one. Since the inboards seem to go easily defective, i would not recommend this.
    I have the jedec file of the 301094-001 PAL if anyone is interested

    -Jonas

  6. #6

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    Quote Originally Posted by stynx View Post
    To address more memory, we would have to swap out the RAS-generator PAL (301094-001) with a new modified one. Since the inboards seem to go easily defective, i would not recommend this.
    I don't follow the reasoning. Replacing an aging part on a failure prone board should only improve its reliability if done with proper technique

  7. #7

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    Are those PALs compatible with new Atmel ones? Like ATF16, ATF22 and ATF1508... PALs are like one of the things that fails after capacitors, which is what kills a lot of Commodore PETs etc... they do die due to age eventually.

    Anyway very exciting development! I think I had messaged you before asking about things in a similar line as Harrison I guess he was justa bit more motivated lol. I'll be wanting to make 2 4 or 8MB variants if that becomes possible... it may also be possible to bodge a wire directly from the CPU address lines if it isn't available on the memory bus already. The more memory on the 32bit piggyback card the better especially for things like running win 3.x on 8bit bus machines!

    Edit: Also I have a batch of 5161 expansion senders... I haven't assembled them but I have most of the parts, perhaps I will have time over the holidays to play with that. Computer reset probably still has a bunch of expansion boxes with receivers.

  8. #8

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    Quote Originally Posted by cb88 View Post
    Are those PALs compatible with new Atmel ones? Like ATF16, ATF22 and ATF1508... PALs are like one of the things that fails after capacitors, which is what kills a lot of Commodore PETs etc... they do die due to age eventually.

    Anyway very exciting development! I think I had messaged you before asking about things in a similar line as Harrison I guess he was justa bit more motivated lol. I'll be wanting to make 2 4 or 8MB variants if that becomes possible... it may also be possible to bodge a wire directly from the CPU address lines if it isn't available on the memory bus already. The more memory on the 32bit piggyback card the better especially for things like running win 3.x on 8bit bus machines!

    Edit: Also I have a batch of 5161 expansion senders... I haven't assembled them but I have most of the parts, perhaps I will have time over the holidays to play with that. Computer reset probably still has a bunch of expansion boxes with receivers.
    You are right by saying that the PALs are aging. I had salvaged 3 RAS-generator PALS (TIPAL20L8, PL20L8 and PAL20L8 ) from different boards but only the last one had (seemingly) all the correct equations. the TIPAL was completely dead and the PL20L8 was part empty and gave a different checksum from time to time. While testing the new memory expansion, my only non-Parity inboard went bad. It now freezes at checking the 256k XMS on the card. I have the experience that even with proper antistatic measures the inboard can turn dead all of the sudden. I may unsolder and read out all other PALs on the dead boards. maybe i can fix at least one of them?

    Up to 16Mb may possible with only changing the 301094 PAL on the inboard. The most straight forward solution would be replacing the 2 RAS-signals for the 2Mb expansion with 2 additional address lines.

    -Jonas

  9. #9
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    Quote Originally Posted by cb88 View Post
    Are those PALs compatible with new Atmel ones? Like ATF16, ATF22 and ATF1508... PALs are like one of the things that fails after capacitors, which is what kills a lot of Commodore PETs etc... they do die due to age eventually.
    The common GALs (16/20/22V8/10s) were specifically designed to be fairly universal replacements for a good selection of earlier PAL devices, at least electrically. (I don't think you can just flash the same .jed files onto them, you'll need to recompile the equations for the newer device.)
    My Retro-computing YouTube Channel (updates... eventually?): Paleozoic PCs

  10. #10

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    I have read out some more PALs. They are hosted

    here.

    Since I own three defective Inbooards and one I of them is very damaged (corroded traces), I will continue to unsolder the PAL-ICs from it and try to get the jedec files from them. We may be able to save some of the currently defective Inboards if every chip can be replaced.

    -Jonas
    Last edited by stynx; November 21st, 2020 at 03:34 PM.

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