Recent content by ab0tj

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...

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.

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...

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...

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.

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...

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...

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...

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...

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...

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.

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...

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...

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