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I recently acquired a Heathkit H8 computer. It only has two boards plugged into the bus: the processor board that every H8 has, and another board, which is apparently a dynamic RAM board.

I can't find any identifying markings on the DRAM board. It has an Intel 8202A dynamic RAM controller, 8 MK4116N 16Kx1-bit dynamic RAM chips (so 16K bytes of RAM), and apparently another 24 open sockets to support up to 64K. I confirmed through the H8 front panel that the machine does have 16K of RAM.

Does anyone know anything about this board? I'd like to know how to set the DIP switches and how the RAM on the board shares the address space with the H8's built-in memory.

I'm pretty sure the board is not the Heathkit WH-8-64 dynamic RAM card, because the description in the WH-8-64 manual doesn't match this board at all (e.g., the WH-8-64 doesn't have the 8202A), and also the manual specifically says the WH-8-64 doesn't work with 4116-type RAMs.

Mysterious Heathkit H8 dynamic RAM board

Much larger photo

Update: I found one image of the same board through Google, a tiny one apparently from an eBay listing:

enter image description here

The listing seems long gone, though.

Update: Found the listing! It doesn't identify the board though.

user3840170
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Willis Blackburn
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    No markings at all is interesting for a commercial board, or even a computer club designed/produced one. – Jon Custer Mar 18 '23 at 21:45
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    My guess is it was a third-party board created by someone who just didn’t think to put any identification markings on it. Probably didn’t think that 40 years later someone would be asking about it. – Willis Blackburn Mar 18 '23 at 23:19
  • The DIP switches likely set addresses (possibly on the bank level). If the card only has traces front and back, and no hidden traces, it shouldn't be that hard to figure them out if you cannot find a manual. – dirkt Mar 19 '23 at 07:02
  • From the eBay pictures we can tell that 8 on, rest off is a good setting for the 8-position DIP switch with 64K, and mine has 1-5 on, 6-7 off, 8 on with 16K. Nothing is really leaping out at me. I suppose I could try switching some of them and see if the 16K of RAM moves to a different address. – Willis Blackburn Mar 19 '23 at 22:29
  • Concur with dirkt, you can follow rhe traces or possibly monitor the RAM chips CS pin to see what address range activates it for a given DIP switch setting. That last one is harder work but should succeed where you can't follow the traces, and the algorithm is likely a simple one. – paxdiablo Dec 12 '23 at 01:24
  • Your link to the eBay listing seems to have died now :-( However, it seems to be the same one as mentioned in my answer, due to the replaced 4 way DIP switch. It is also of around the same time... – Greenonline Dec 18 '23 at 20:01

2 Answers2

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Interesting. I know of at least 3 different 64 KiB Cards (*1) for the H8, but none of them using a 8202.

The usage of a 8202 is a clear indicator for a rather early board, which the WH-8-64 is not, as it was introduced as late as 1982. It also was only sold with a minimum of 32 KiB (at 449 USD).

*1 - There are as well several newer CPU+RAM boards for the H8 bus, usually Z80 with static RAM.

*2 - The WH-8 is the fully assembled version of the H-8 kit.

Raffzahn
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There is an article on Hackaday, Versatile DRAM board adds memory to any Heathkit H8 variant, about a board, such as yours, that was on eBay (probably the same one as you found the link to, going by the photo, especially the replacement DIP switch):

DRAM board (front)

He found this on eBay, where a few vintage H8-compatible DRAM boards were for sale. Although [Scott] didn’t manage to win the auction, the eventual buyer was kind enough to snap some high-resolution pictures of the board which enabled him to reverse-engineer the circuit. The board used the similar D8202 DRAM controller and came with logic that generated the proper signals to interface with the 8080 and 8085 CPUs.

However, as mentioned above, the 4 way DIP switch looks as if it may have been replaced at some point.

There is a little more information about that same board, and a photo of the rear of the board, in the blog, Designing a DRAM board for the Heathkit H8 Computer using the Intel D8203 DRAM controller, under the section, Solution 1: Some random eBay board to the rescue!:

DRAM board (rear)

Around this time, some H8 DRAM boards appeared on eBay. I lost the auction. But by virtue to creating youtube videos and generally pestering people on forums, I eventually made contact with two people who acquired these vintage 8202-based DRAM boards.

With the help of the community, I reverse-engineered this board without ever having one in my physical possession.

For completion, the same guy shows the derived design and build of his 8 MB (!) board in Heathkit H8 Part 4: 16 Megabytes of RAM in a Heathkit H8 Vintage Computer:

Recently designed 64 kB RAM board

This is the Les Bird H8-64-2 board (as listed in Raffzahn's answer):

Les Bird H8-64-2 board

Apparently, this board may be a little glitchy (with the 8080 processor board), as mentioned at 8:33 in the above video, so hence why the new 8 MB board was designed, with the design being derived from your board.

There is also a Github repository for the new board: sbelectronics/h8/h8-dram. Some additional technical details about your original board are also listed there.

Maybe leave a Github issue (or a comment under the YouTube video) inquiring as to whether he has any other further information about the original board..?

Greenonline
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