Category Archives: Retrocomputing

RC2015/07 entry – vector display system

For RC2015/07, I’m going to hook up an old vector display (the retro part) to a modern microcontroller and either write a new game for it or port an old one. Vector displays were used on computers from the 1950s … Continue reading

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Pacer control panel interface card schematic

I’ve nearly finished tracing the Pacer control panel interface card schematic.  I haven’t yet traced the connections of one NOR gate of the 7425 at position 6A, and one inverter of the 7404 at position 5C. It’s possible that they’re … Continue reading

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Pacer user memory card schematic reverse-engineered, and status of the card

I finished tracing the Pacer user memory card schematic. Most of it seems fairly obvious, except bus pin 25 and the E1/E2/E3 jumper. There are also some functional problems with this particular card.

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MM5204 to 2716 EPROM adapter

The PACER memory board has sockets for four MM5204 512×8 EPROMs. The MM5204 is somewhat hard to come by, so I’ve designed a small adapter board to plug into an MM5204 socket and accept a common 2716 EPROM.  Only the … Continue reading

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Bad RAM; attempting to dump PACER monitor ROM

At present the RAM on the user memory board in the PACER isn’t working correctly; the four most significant bits (D15..D12) are always reading as ones. Since this is true for all four banks of RAM (0000-00FF, 0100-01FF, 0200-02FF, and … Continue reading

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PACE assembler and simulator

I’ve created a Github repository for my PACE assembler and simulator, which together with some very incomplete support for National’s IMP-16 multi-chip processor, I call ns16.  It is released under the GPLv3.  This was all work done back in 2009 … Continue reading

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Reverse-engineered schematic of PACER CPU card; PMOS data bus sensing

After quite a few hours with a continuity tester and magnifier, I have the PACER CPU card mostly figured out, and have drawn a schematic . I haven’t identified all of the passive component values, and there are probably other … Continue reading

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FIG-Forth for the National Semiconductor PACE 16-bit microprocessor

One of the things I’d like to accomplish in RC2015/01 is to get some non-trivial software running on the PACER. In addition to hardware restoration work, this will require building a memory expansion, because as supplied it only has 1Kx16 … Continue reading

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First actual RetroChallenge work on PACER

I’ve written about what I did with the PACER before the RetroChallenge, so henceforth I’ll describe what I’m doing for the RC. I’m starting with tracing out a schematic of the motherboard/backplane, including the power supply, the eleven edge connector … Continue reading

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More pre-RetroChallenge PACER status – fuse holder, power supply

I found some of my notes from August, so there are a few more details about the state of the machine, and preparations made at that time, particularly relating to the fuse holder and power supply.

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