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Odd extended ISA slot - 32-bit memory expansion pin-out

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    Odd extended ISA slot - 32-bit memory expansion pin-out

    I have a Northgate 386/20DX system I bought in 1989. I'm pretty sure the case frame, PSU, and motherboard all came from the Taiwanese clone makers at the time. The front panel was branded Northgate and that was the extent of their contribution.

    Two of the ISA slots have the normal 62 pin 8-bit ISA card connector. But behind the slot instead of the normal 36 pin 16-bit ISA extension, there is an 80 pin extension for 32-bit memory expansion boards. Looking at the solder points and traces, the first 36 pins seem to be ISA 16-bit signals. However I'm not sure what the later 44 pins are. From the AT keyboard connector out to the far edge, the slots I have are 16, 32, 32, 16, 16, 16, 8, 16. I've seen this same configuration on other clone MBs. Shy of pains-taking ohm meter examination, does anyone have a quick idea where I can get the 32-bit pin out?

    Also any idea if there is a memory select feedback present on one of those pins that would short circuit the wait state generator and allow that memory to run at 20 MHz x 32 bit?

    The only real identifiable markings on the MB is '20 MHZ 386 PAGE MODE" on the silkscreen. It has an AMI BIOS and room for 4MB on the MB with discrete 70ns DIPs.

    Thanks.
    "Good engineers keep thick authoritative books on their shelf. Not for their own reference, but to throw at people who ask stupid questions; hoping a small fragment of knowledge will osmotically transfer with each cranial impact." - Me

    #2
    Very common in the early 386 era. I have an Everex board like that as well as a Mylex one. Unfortunately there was no standard for these, not even within a manufacturer's own products.

    I have a 386DX/20 board were all the memory is on one of these boards--nothing on the planar at all.

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