Hum... my programmer got here, and so did the EEPROMs and the controller, but things are just not going well...
First of all, I built an AT2XT converter. Did not order the PCB, so I just breadboarded it like this:

And it works!!!!
But... for the rest:
1- The controller seems to be busted. It did not work when it arrived (neither in this board nor in a Pentium machine with the onboard FDD controller disabled). Today I put it on the 8088 PC again to test it one final time and BAM, my floppies were seeking and stuff was working.... until I turned the PC off and on again, then they went back to not working at all
2- The EEPROM doesn't work. It simply doesn't POST with the W27C257 in the socket.... Oh, it actually does POST if I flash the machine's regular BIOS (which I read from the 27128 BIOS chip) to the last 16KB of the W27C257 AND leave the original BIOS chip in its socket (it doesn't post if the EEPROM is there by itself) - and in all cases the Option ROMs are completly ignored. What sorcery is this? I imagine, from my results, that you are not supposed to have both EPROMs there at the same time, but why wouldn't it POST then with the W27C257 by itself?

Btw, I backed up the original BIOS and will update the first post accordingly.

Quick update: I bought a new Prime 2 (not 2C as the first one I got) and this one works. I think this one is even better, as it has a jumper that selects if the card is in an 8-bit or 16-bit slot, so I'm positive the IDE port will work with in my XT machine. Interesting fact: I won't need an HD floppy ROM, I just put an MS-DOS 6.22 installation disk (1.44MB) and, while the setup did not start (as I only have 256KB installed), the floppy booted to the prompt succesfully and everything seemed fine. I'd guess that if the BIOS did not support HD floppies, it wouldn't have booted at all, so this is a plus.

alexanrs wrote:

2- The EEPROM doesn't work. It simply doesn't POST with the W27C257 in the socket.... Oh, it actually does POST if I flash the machine's regular BIOS (which I read from the 27128 BIOS chip) to the last 16KB of the W27C257 AND leave the original BIOS chip in its socket (it doesn't post if the EEPROM is there by itself) - and in all cases the Option ROMs are completly ignored. What sorcery is this? I imagine, from my results, that you are not supposed to have both EPROMs there at the same time, but why wouldn't it POST then with the W27C257 by itself?

Hi Alexan, the 27256 socket is not designed for option ROMS or to work independently from the main BIOS socket as it is probably not mapped into the proper memory area locations. If i can place a bet it is mapped to start at F600h or F800h which is where IBM Cassette ROM BASIC was meant to be placed. See this thread for details:

ROM BASIC on XT clones

In any case if you do want to try ROM BASIC and burn an EEPROM with just drop me a PM and i'll send you the file ready to burn.

Hi Alexanrs.
How are you?
I'm from São Paulo.
I would like to know from who you bought this board.
I'm going to buy the same board. If you can, please, send a message to israelgino@outlook.com
Thanks a lot.

I bought this a few months ago, sold here as an Octek brand.
http://www.ebay.com.au/itm/New-Old-Stock-Ockt … %3D222220854536

I’ll add some info on this board. I picked one up myself from a seller in Canada.. Was in a lot of other boards. I don’t have all the proper tools to test mine but I think it is ok. I get LCD initalization with a 16 bit isa card that is known to work in 8 bit slots. No other monitors available to me right now so out of range errors are I get.

Some digging shows this also known as a HEDAKA HED-918: http://stason.org/TULARC/pc/motherboards/H/HE … 88-HED-918.html

Looks like mainly a Russia board imported elsewhere?

Throw this into google search: HED-918 site:www.phantom.sannata.ru
And run the results through google translate adds some info.

Anyone in this thread who has the board make any progress? Curious to see what people got up to with it.

Hello guys! What the best graphic card will be for Turbo TD-20 motherboard (IBM XT with Siemens SAB-8008-1 processor)? I have exactly the one in the picture form the beginning of thread. It seems to be in very good condition and I hope it will work. I need just ISA graphic card.

The memory interface on that board is fascinating! You can choose between 424256 chips (which are 256k x 4) or 421000 chips (which are 1M x 1), and also a single 256K x 4 chip. So in no way you can build a byte-wide x8 memory bus from that. Instead, it looks like the memory interface is built around 4-bit access, and it splits every 8-bit cycle from the 8088 into two 4-bit cycles (most likely handled in page mode) to the RAM chips. If you consider the memory to be nibble-based, it starts to make sense. U3 always is a 256k x4 bank providing 256k nibbles, whereas U4-U7 either make up one 1M x 4 bank providing 1M nibbles, or four separate 256k x 4 banks, providing 256k nibbles each, which is 1M nibbles in sum. Together with U3, it is 1024K nibbles + 256K nibbles = 1280K nibbles = 640 KBytes.

It doesn't look like the board offers 10MHz operation, though. The crystal of 28.628 MHz is perfect for doubled XT speed, which is 9.54MHz. For 10MHz, you would need a 30MHz crystal.