I just wanted to share my success in building the Xi 8088 for those who are hesitant about taking this project on. I did have some stability issues as first, but after building SMBaker's active termination board, it has been soak tested on turbo (8 mhz) for hours without hanging once. A few observations or things which I think helped:

I noticed in another forum thread about the project that Sergey emphasised using F series logic for U15 to U23. Although ACT are mentoned on the build page and can work, it seems like F is preferred.

When building the termination card, I followed appendix B of this document to determine which lines should be terminated. Basically, that means isolating legs on the resistor packs for all IRQ and DRQ lines, plus I/O CH RDY. I used 220 ohm packs.

There is a newer version of the BIOS on Sergey's github which you can assemble. While most of the improvements relate to the Micro 8088, there are some which affect the Xi 8088 so it is worth doing and you can inject the latest XT IDE universal bios version while you're at it.

I don't have a ton of cards plugged in, so it's possible I could start to have issues with all slots populated. I have no use for upper memory or adlib support though.

So the termination is simply 220R to +5V on all IRQ/DRQ lines and IOCHRDY?

maxtherabbit wrote on 2022-05-14, 14:23:

So the termination is simply 220R to +5V on all IRQ/DRQ lines and IOCHRDY?

No, the other way around - I terminated all lines on SMBaker's pcb except those. This is the active terminator board regulated to 2.7v, using 220 ohm packs. Anything that said NC on the table in the linked pdf, I cut the leg off the resistor pack and covered it with electrical tape.

SanguineBrah wrote on 2022-05-14, 15:37:

maxtherabbit wrote on 2022-05-14, 14:23:

So the termination is simply 220R to +5V on all IRQ/DRQ lines and IOCHRDY?

No, the other way around - I terminated all lines on SMBaker's pcb except those. This is the active terminator board regulated to 2.7v, using 220 ohm packs. Anything that said NC on the table in the linked pdf, I cut the leg off the resistor pack and covered it with electrical tape.

I have no idea what "smbaker's pcb" is or where to look for it so I'm blindly guessing here

maxtherabbit wrote on 2022-05-15, 03:00:

I have no idea what "smbaker's pcb" is or where to look for it so I'm blindly guessing here

It's mentioned earlier in the thread but I guess it's a lot of pages now. Link

My Xi 8088 is alive! (again) My Xi 8088 build worked like a champ, but then after a year or so it wouldn't even post - no activity on the bus at all. So it sat for years. Recently I took another shot at it... The soldered joints "looked ok", but for kicks I redid them ALL. Plugged it back in, and booted right up. Go figure, I knew my soldering skills were lacking. If it helps anyone struggling - double and triple check your solder connections and don't trust "it looks ok"!

Anyone have a creative idea for a case for your build? Right now it's in a beat up 30+ year old beige case but I'd prefer something to show it off. I was thinking maybe one of the open motherboard concepts. Anyway, just curious what others are using and if there are any active builds of the Xi 8088 going on. It's quite a challenging build, my next step is to get off using the floppy and install an isa-cf card.

I just updated the BIOS version from 0.9.0 to 0.9.9 and there is now 16 second delay before the machine posts. Is this normal? EGA card being used. None of the dip switches or presence/absence of cards seem to affect this behavior.

Hello guys! can anyone recommend a case to mount micro8088?

bazingaa wrote on 2023-06-26, 10:37:

Hello guys! can anyone recommend a case to mount micro8088?

What type of backplane are you gonna get/use? this determines the size of said case. or you could even make your own 😁
I got a original IBM 5160 case (sold for "sleeper" builds). current backplane only has 3 isa slots and no power, kinda have to hack it anyway. miniATX towers can be cute 😁

CodeAsm wrote on 2023-06-26, 13:16:

bazingaa wrote on 2023-06-26, 10:37:

Hello guys! can anyone recommend a case to mount micro8088?

What type of backplane are you gonna get/use? this determines the size of said case. or you could even make your own 😁
I got a original IBM 5160 case (sold for "sleeper" builds). current backplane only has 3 isa slots and no power, kinda have to hack it anyway. miniATX towers can be cute 😁

I have Segey's backplane, https://github.com/skiselev/isa8_backplane
I was thinking about getting a microATX case but my worry is that only got 4 expansion slots and it would be full for external interfaces.
May be full ATX with 7 slots would be useful ?

I plan to use below cards.

CPU - micro8088
VGA - Trident 8900CL
Sound - PICOGUS OPL2/GUS
NIC - I have few ISA 16bit ones, need to check compatibility
UART (+USB mouse) - may be this https://github.com/hkzlab/ISA_DualUARTParport + https://github.com/LimeProgramming/USB-serial-mouse-adapter
XTIDE - May be this https://github.com/glitchwrks/xt_ide/tree/rev_4 (I have PCB for this, but not sure about soldering CF slot https://github.com/monotech/monotech_xt-cf-mini)

I only found one IBM 51xx cases on ebay and it is $200, I am not from USA and they are pretty rare here.

If anybody is building a Xi 8088 and has been having an issue dialing in the frequency of the OSC crystal, I have a suggestion. On both of the boards I have built, adjusting C54 would give a much higher frequency than required, making it impossible to get to 14.31818mhz. My assessment is that this is a result of the load capacitance being too low on one side. While the values of ~33pf on either side of the crystal (C52, C53) are calculated correctly, the addition of the trimmer in series with C53 significantly drops the capacitance on that side of the crystal. I found that swapping C53 with a 100pf part, and C54 with a 60pf trimmer together yeild something in the ballpark of the 33pf and make it possible to hone in on the required frequency.

Moogle! wrote on 2023-05-06, 03:41:

I just updated the BIOS version from 0.9.0 to 0.9.9 and there is now 16 second delay before the machine posts. Is this normal? EGA card being used. None of the dip switches or presence/absence of cards seem to affect this behavior.

It might be it looking for a PS/2 mouse, I have a similar problem with my xi8088 derived XTjr 8088 based machine. Try plugging in a ps/2 mouse and see if it boots faster. This pause used to trip me up a lot on my custom build when testing, I kept thinking I'd broken something! I mean to edit my custom bios to see if I can reduce that delay...

Having completed a second Xi 8088 build, I have more to add. I encountered a lot more stability issues this time. It seems like there was a big jump in instability when plugging in older ISA cards using lots of TTL chips. For example, stability was fine using a Trident VGA card but swapping to an original IBM CGA card caused a lot of faults.

I also found that the choice of CPU made a big difference in stability. I have had major issues with 3 different Oki 80C88-2 from a variety of sources (some likely legit, some questionable) but then switching over to a V20 or what I am using now, which is a Fujitsu MBL8088-1, caused a significant stability improvement. It is tempting to chalk this up to supply issues but I am not so sure.

When experimenting with SMBaker's active termination board, I found that stability was better with the voltage set a little lower (2.5v vs the 2.7v mentioned in the blog post). It is possible that more tweaking or different termination resistors could improve things further.

Curiously, I have found that clock frequency plays no role in the likelyhood of errors - all tests are the same in turbo mode (8mhz) as they are at 4.77mhz. I am at the stage now where stability is rock solid with the CGA card, XT IDE and Sergey's floppy/serial card but if I add a vintage parallel/serial card, Checkit's RAM test will throw up errors after an hour or so.

Good day !
First, I'm showing off a little: I finally assembled Kh8088, which had been working for a long time, into a case. For some reason, I love 19" cases)))
In the photo: Xi8088 by skiselev, CGA Redux by hkzlab, OPL2 and FDC by skiselev, VCF XT-IDE Rev 2 and ISA Backplane by Alexandru Groza.
However, there were not enough free slots to add a network card and and EMS card. I will have to do a little more metalwork to move the COM2 and CF card to a separate panel and free up two slots. But that is an optional option.
But there were several shortcomings that I (perhaps) did not pay attention to earlier, or they did not appear earlier.
1) During a "cold" start, the Xi8088 "hangs" at POST 08h for 20 to 40 seconds. Then it boots normally and during "hot" restarts this problem does not occur. I already found information about this problem in other discussions. There, as a reason, they indicated the need to use 82c59 of specific manufacturers, namely AMD. Unfortunately, I only have a Toshiba 82c59 at the moment. I have already ordered several sets of different 82c59, even including the ex-USSR KR1810ВН59А - so I will experiment. But maybe someone has already found other ways to solve this problem.
2) Periodically (quite often), 1.2 MB and 1.44 MB disk drives do not work well. That is, they work - write, read, copy from one to another. But when trying to format the diskette, the most various errors are issued. It is sometimes possible to make a system diskette by chance in one case out of ten. And then after that it is not always possible to boot from it. This is definitely not a disk drive problem or a controller problem - everything works fine on any other motherboard. Alexandru Groza wrote about the same problem with his 386SBMC project - and yes, I also faced the same problem with his 386SBMC. Alexandru Groza believes that the matter lies in the timings on the DMA. I have Xi8088 almost completely assembled on K1533 (74ALS), and maybe it is worth trying to replace Page Registers and X-Bus Transceivers with 74F? - simply, apart from the incorrect operation of disk drives, no other problems arise...

mogwaay wrote on 2023-07-27, 21:42:

Moogle! wrote on 2023-05-06, 03:41:

I just updated the BIOS version from 0.9.0 to 0.9.9 and there is now 16 second delay before the machine posts. Is this normal? EGA card being used. None of the dip switches or presence/absence of cards seem to affect this behavior.

It might be it looking for a PS/2 mouse, I have a similar problem with my xi8088 derived XTjr 8088 based machine. Try plugging in a ps/2 mouse and see if it boots faster. This pause used to trip me up a lot on my custom build when testing, I kept thinking I'd broken something! I mean to edit my custom bios to see if I can reduce that delay...

I did something and it randomly stopped doing this. Don't remember what though. 😒