That's really cool! Thank you very much! 😎👍

love it, thanks for sharing!

this might be useful for XTIDE?

Yes, I think so.

4xtx wrote on 2021-08-18, 11:50:

this might be useful for XTIDE?

yes it will
you can program XT-IDE to use the normal IDE ports and disable IDE or HDD on bios: then xt-ide will take over and you'll have large drive support

Yes, I designed this for that specific use in one of my XT systems. Still waiting on my PCB's from JLC.. don't know what the shipping holdup is. Seems like I've been waiting forever.

Might be worth telling some retro PC Youtube channels about this, I know some have had needs for BIOS mods in the past and had to either modify the BIOS on board or use something like an old Ethernet card.

And just as I said I felt like I've been waiting forever, the mail dude brought a JLCPCB package.. I'll order the components to get this tested.

If I bypass the power on pin 1 of the eeprom, and wire eeprom pin 1 up to ADR15 & P0 (pin 3 & 2 ) of the 74LS688, can this be used for a 64K eeprom?

I believe you would just need to run pulldowns from A13 and A14 on the ROM to pin 7 and 9 respectively on the 74LS688 chip to keep the address lines low during a read. But hopefully someone else can chime in to confirm that works. I haven't ever tried that.

hmm.. nevermind, I think that would work for a 28C64and not a 27C64. Not sure you could accomplish that on a 27C series. I would have to redesign it for 28C series chips.

Regardless, a 27C256 OTP is only about $2.30.

wiretap wrote on 2021-08-18, 21:02:

hmm.. nevermind, I think that would work for a 28C64and not a 27C64. Not sure you could accomplish that on a 27C series. I would have to redesign it for 28C series chips.

Regardless, a 27C256 OTP is only about $2.30.

I guess I should've mentioned a 27C512 ... 64Kbyte .

Oh, bytes.. 27C512 should work if you write a 32KB bin with a double image to fill the 64KB EPROM.

As far as using the whole capacity, I'll have to take a look this weekend. I'm currently on the road.

Also, I think I may need to revise the pull up to a pull down on the address jumper config of this board. It will work as is, but the jumper on/off is reversed for the addresses on the silkscreen. I only glanced at it before I left the house earlier, but I'll release a rev 0.2 if that's the case to correct it.

EEPROM version added to the first post. Also supports the 27C64 / 28C64B. Boards ordered for testing.

wiretap wrote on 2021-08-20, 20:23:

EEPROM version added to the first post. Also supports the 27C64 / 28C64B. Boards ordered for testing.

Neat, but... I was gonna say something about the addressing, but at first glance you took that into account, yet looking at the schematic... ? I'm off to bed, I'll try to understand it tomorrow.
either way, Neat. waiting for the version that has 64KiloByte support 😋

It needs a pulldown to be zero for the address. In the first rev of the mini board, I used a pullup. No big deal, but the 1 vs 0 will be backwards so the silkscreen would be reversed as to what the jumper is set too. I corrected that already, but I'll just double confirm by building one before uploading the files. My parts should be here next week.

wiretap wrote on 2021-08-18, 19:34:

And just as I said I felt like I've been waiting forever, the mail dude brought a JLCPCB package.. I'll order the components to […]
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And just as I said I felt like I've been waiting forever, the mail dude brought a JLCPCB package.. I'll order the components to get this tested.

awesome - please share a photo of the finished product 😀

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.