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    Memory board for the IBM 5170

    Agreed, that would be a great way to go about it. The problem I ran into when exploring SRAM-based options is the control logic that goes into making it work... You have to deal with the fact that reading vs. writing the SRAM involves an entirely different set of data and address signals, along...
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    Memory board for the IBM 5170

    Correct. The CPLD I'm using at the heart of it can barely handle that as it is... I may look into EMS4.0 support in a later version of the board.
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    Memory board for the IBM 5170

    I guess in my mind it is a verb here, "backfill enable" meaning to enable the board to backfill memory in those areas. But I'll keep that in mind for v0.2 of the board...
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    Memory board for the IBM 5170

    The backfill switches add system memory independently of the EMS page frame. It's not likely the "0-128k" setting will ever be used, but turning on switches 3, 4, and 5 would bring a 256k system up to 640k for example. EMS is a separate thing and shows up in a 64k block of memory that will be...
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    Memory board for the IBM 5170

    That's the term used by most expansion memory boards, at least that I'm familiar with. See the manual for the AST RamPage Plus 286, for example.
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    Memory board for the IBM 5170

    Hi all, Just wanted to share what I've been working on lately. This is a 16 bit ISA expansion card that provides 8MB of system RAM and 8MB of EMS RAM. It uses 30-pin SIMMs, because I have always used SRAM for projects and wanted to play around with DRAM for once. Boards have been ordered and...
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    IBM EGA Card Memory Expansion Boards

    Hi all. One of the projects I have been working on lately is recreating the PCB for the IBM EGA memory expansion board (part number 6480099). I'm going to have board made either way to expand my own system, but I was wondering if there was a need out there and I should get extras? They seem to...
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    Roast my design: 16-bit ISA memory board

    So this may shed some light on it. Looks like MEMCS16# is latched by ALE on the 5170 motherboard. The latched signal goes into a PAL which seems to be doing the data steering stuff. Sooo, it looks like one would have to beat ALE going back low in order to get 16-bit transfers. That would explain...
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    Heath/Zenith 150-303 EGA Card

    Hi all. I ended up with one of these cards but the system doesn't boot with it installed. I'm not seeing anything physically wrong with it but the BIOS EPROM is missing the cover over the window, so I'm wondering if it might have been partially erased over the years. Does anyone happen to have...
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    Roast my design: 16-bit ISA memory board

    Inspired by the Lo-Tech 1MB RAM board which is great for adding UMBs to XT class systems, I set out to design a 16 bit version for AT class systems. It can selectively fill 0-512K in 64KB chunks (which is probably already maxed out on most ATs) and 512-1024K in 32K chunks, though obviously some...
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    WTB/WTT: IBM 5154 Monitor

    I recently acquired a IBM 5170 machine and would like to get a 5154 monitor to match. Will pay a fair price plus shipping, or I have some items I could trade including an Apple IIGS or SGI Indigo system. Maybe something else, let me know what you're looking for.
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    RTC Support?

    Hi all, I'm finally to the point of adding RTC support to the "CheapBus" system I've been working on (see here if interested). Looking at the way CP/M expects the date to be formatted, I wonder if it is going to handle the year correctly? Has anyone implemented this and what do I need to look...
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    Looking for Tarbell Cassette Interface Schematic

    Does anyone have a good copy of the schematic for the Tarbell cassette interface? I'm trying to recapture it in KiCad so I can make a PCB for a quasi-replica. I have found a couple PDF copies of the manual online, but they are scanned at fairly low resolution making it hard to make out some...
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    Wanted: IMSAI 8080

    I'd like to give an IMSAI 8080 system a good home. Working or not. Looking to spend US$2000 or less. Thanks.
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    Wanted: MPU-401 or MPU-IPC

    I am working on building an MPU-401 clone device. It would be good to have "the real thing" to test against, so I'm looking for an MPU-401 (with or without interface card) or MPU-IPC(-T) (with out without breakout box). Please let me know if you have or know of one for sale for a reasonable...
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    HardMPU <working title>, anyone here an EE?

    Hi all, Since it seems to be almost impossible to find a real MPU-401 or compatible, I am going to attempt to create my own. Once the design is complete, the hardware and software will be open source so others can build them. I am also going to try to offer boards and/or kits for sale (but NOT...
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    Swap terminal version Model M keyboard (and terminal?) for PC version

    I have this Model M keyboard, P/N 1392595 that I acquired with a 3127 terminal. It has an RJ45 connector on it. I plan to"convert it for PC use, but before I do that I figured I should check if anyone wants to swap for one that is already set up to plug in to a PC. I'd even include the terminal...
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    Tandy 1000 EX complete system with memory upgrade

    I bought this system a long time ago at a thrift store, but I just never use it. It includes the main system, color monitor, memory upgrade board (for a total of 640K RAM), external 3.5" floppy drive, and a DOS 6.22 boot floppy. Everything works good with the exception of sometimes the internal...