wiretap wrote on 2021-08-29, 03:04:

Here's the first rev of the first board soldered up. I'll setup a system to test it on and flash a BASIC ROM for testing. This i […]
Show full quote

Here's the first rev of the first board soldered up. I'll setup a system to test it on and flash a BASIC ROM for testing. This is really the first day in about a week I've been able to have 20 minutes free.. haha. I've been covering for my manager at work while he's on vacation and it's been some lovely 18hr work days. I hope to have Monday free to get this tested, but no guarantees. My wife starts back to college Monday, so I'll have to keep my 4-year old occupied as well. Busy times 🤣.

Thought I had some 20-pin sockets for the 688 chip, but apparently not. I'll have to order some.

Hi! Would you be so kind and share the BASIC ROM you've used? I cannot find working one... Thanks!

I built this cute little card, but ran into a problem, the address selection jumper doesn't work, the address is always D800h.

Thank you, this card is very useful. I built one for my 386 which doesn't support LBA, to use the XTIDE BIOS instead. Works great!

I didn't have the binary comparator chip in a DIP package in my parts bin, so I dead-bugged a SOIC. Also the resistor footprint seems a bit too small for the common 1/4W resistors.

What is the largest rom that can be used this way? Is it possible to have one that boots a OS? Like freedos or dare I say. Windows?

A rom/cf card would probably be more practical

But as a thought experiment.

Having dual rom, that had xt-ide and memtest would be cool also.

This is a very simple card with no mapper chips.

As such, the largest contiguous block allowable would be 1 full segment, or 64k.

The IBM PC specification only allotted for 384k of "adapter rom region" between 640k base memory and the top of the first megabyte.

ROM-DOS cards use a method called "bank switching", which use a small "window" in this adapter region (usually 32k or 64k in size), with some means of remapping which part of the ROM-DOS card's disk image is mapped to this window, usually by writing to an IO address with an instruction word.

Again, this card is very simple, and has no mapper. 64k is the theoretical maximum.

Reminds me I still need to build this..

Sphere478 wrote on 2023-11-25, 04:41:

Having dual rom, that had xt-ide and memtest would be cool also.

Dual rom cards are availabe, as open source DIY or can be bought from Monotech:
* https://github.com/monotech/ISA-DoubleROM
* https://monotech.fwscart.com/product/doublero … le-rom-isa-card

Depending on the size of the option roms you wish to have installed, burning two or more into a 64k rom is a possibility.

I made this card and had a strange problem, when using 28C256, the address is always D800, after changing to 28C64 or 27C64, the address is always DE00, the jumper does not work, can anyone tell me why this is? Maybe I should replace the 74LS688 with the 74HCT688?

PS:
Something magical happened, I got a few pieces of MM74HCT688N, replaced the SN74LS688N with it, and then everything worked fine, the address jumper worked correctly, 0xC800, 0xD000, etc. were available.
I'm using an EEPROM PCB, 28C64B.

appiah4 wrote on 2023-11-25, 07:47:

Reminds me I still need to build this..

OK, so I got around to building it:

A few questions:

1. I see there are polarity markings for the capacitors. I used 100nf ceramics, and I see other builders also have done the same. I am thinking this should not be an issue in a DC circuit, right?
2. I'm not sure I get how the memory location jumpers ought to work. I need to look at my PC's memory map and locate 64K of free memory at a specific location, then jumper the card accordingly, right?

Cheers,

Ideally, to avoid having multiple devices trying to drive the bus, you want a region with nothing mapped in it. (Even RAM).

There are various tools to visualize the 1st megabyte of memory, but msd is stock in dos6.22

Run it with no memory managers.

Phoboss1976 wrote on 2023-01-20, 19:41:

ignore my previous posts. The small card works like a dream. Obviously I made a mistake when I used the incorrect XTIDE bin. If […]
Show full quote

ignore my previous posts.
The small card works like a dream. Obviously I made a mistake when I used the incorrect XTIDE bin. If you look at the picture It only works where the jumper is set to. I tried it in 3 different machines. 2x386 and a 486 machine. The card works with 27c128 and 27c256. Whichever chip you use you will have to make the bin file to fit into the chip.

The bigger card? Hmm. It does not want to work yet. I have the correct chip. I have the correct bin. I just need to find the address where it wants to work.
Follow up.

Both type of cards are working.
Found the address. I use AT28c64. Only the first jumper needed.

Thank you! I could not get my machine to post with the board until I tried your jumper setting.
Working well now with a 27C128 chip.

Many thanks to the OP for the design, happy days!
-(e)

@wiretap someone made a YouTube vid on your board: https://m.youtube.com/watch?v=WTBoUmHI0pU

Got the PCB's I ordered in today. I went with Blue.

Hi everybody!

I built the "Mini ISA Rom Card" and i am very happy with it. I am not posting very often but i think i can contribute to this beautiful project.

!Be aware, the jumper settings table on the solder mask is incorrect.

This is a full list of all possible combinations of the jumpers on the "Mini ISA Rom Card", left to right (0=unset, 1=set)
---------------------------------------------------------------------------------
0000=F800: TOO HIGH FOR OPTION ROM, DO NOT USE!
1000=F000: TOO HIGH FOR OPTION ROM, DO NOT USE!
0100=E800: TOO HIGH FOR OPTION ROM, DO NOT USE!
1100=E000: TOO HIGH FOR OPTION ROM, DO NOT USE!
0010=D800 (D800-DFFF): VALID 32K BLOCK
1010=D000 (D000-D7FF): VALID 32K BLOCK
0110=C800 (C800-CFFF): VALID 32K BLOCK
1110=C000 (C000-C7FF): VALID 32K BLOCK
0001=B800: TOO LOW FOR OPTION ROM, DO NOT USE!
1001=B000: TOO LOW FOR OPTION ROM, DO NOT USE!
0101=A800: TOO LOW FOR OPTION ROM, DO NOT USE!
1101=A000: TOO LOW FOR OPTION ROM, DO NOT USE!
0011=9800: TOO LOW FOR OPTION ROM, DO NOT USE!
1011=9000: TOO LOW FOR OPTION ROM, DO NOT USE!
0111=8800: TOO LOW FOR OPTION ROM, DO NOT USE!
1111=8000: TOO LOW FOR OPTION ROM, DO NOT USE!

There are really just four valid jumper settings out of sixteen possible combinations. All the other addresses wouldn't be recognized as option roms or even cause address conflicts with other resources. The reason is the huge rom size of 32K and the designers choice, to map the full size of the rom. The rom is directly attached to ADR0-ADR14 (which is 32K). With this low count of parts, it was kind of mandatory to use ADR15-ADR18 for address comparison. But only four combinations of J1-J4 wich are used to compare to ADR15-ADR18 end up in the address range for option roms.

On some very old systems, e000-e7ff is valid for option roms.

PCjr for instance, allows even F000-FFFF on its cartridge ports, permitting full system bios replacement this way. Some carts are designed to load from E000, and are basically just bootable option roms.

More recent systems with large system roms, and ESCD data living there in the e000 neighborhood would have issue, but an old 286 or something should be just peachy.

Well this won't work for the PLOP boot manager I was hoping to use its a 64KB image so I'd need a 27c512 chip. Guess At Least I'll have something I can put xtide on.

Let's throw some peppers here at this project to see if people get excited, I'm creating a board with an options menu and some utilities, format tools, ram test, video, among others, I already have something functional but it's still progressing....

dexterff8 wrote on 2024-09-06, 00:48:

Let's throw some peppers here at this project to see if people get excited, I'm creating a board with an options menu and some utilities, format tools, ram test, video, among others, I already have something functional but it's still progressing....

here is a .ROM to put on the mini iza board and play PONG
soon more tool for RAM testing 😉

https://drive.google.com/file/d/1KQrS3PsX2AVX … iew?usp=sharing

the memory is a 27c256 with 32k