Is the ISA bus speed on this board a set value, or is it tied directly to CPU speed?

I can't make heads or tails of the schematic in this regard, mostly because I'm not entirely sure what the "ISA bus speed" means. I don't see anything on the standard ISA pinout diagrams that shows any sort of "clock" provided except pin B30 which is the 14.31818mhz signal from the oscillator.

*edit*

Ah, I see that B20 is the bus clock, and ont he schematic that is "CLK", which is an output from the 8284.

http://www.jameco.com/Jameco/Products/ProdDS/52871.pdf

This says it'll be a 5 or 8mhz output from a standard 8284, OR a 10mhz output from a 8284-1.

So that makes me think that the bus speed is independent of the absolute CPu speed, which makes me really wonder why my EGA/CGA cards aren't working at cpu speed 10mhz, but do at 8mhz.

BUT, then it also says that the frequency of the ic is in sync with the CPU, so I have no idea.

*edit2*

OK, so I learned a little more about schematic reading.

The turbo oscillator is connected to the 8284's "External frequency in" pin. In the datasheet EFI is stated to be "three times the CLK output". The CLK output is directly tied to the ISA bus on pin 20.

I think this must mean that the ISA bus runs at TURBO OSCILLATOR/3, which at 32mhz chip is a little over 10mhz bus speed.

This would probably explain why the EGA/CGA cards aren't working properly.

Bloodycactus, that also might explain some of your weirdness since you also installed a 32mhz turbo oscillator as I recall. It might also be worth checking that your 8284 chip is rated for >8mhz; the NEC UPB8284AD I bought says it is OK up to "25mhz" but I'm not sure if that's EFI or CLK out...

I think it would be in the best interests of stability to stick with 24mhz turbo oscillator.

Since I had to repair that trace from the speaker connector to U31 (74ALS74), I'm contemplating adding a fuse to that circuit. Obviously the voltage is 5v, but I'm not sure what a good amperage would be.

The speaker is rated at 40ma max.
http://www.mouser.com/ds/2/334/AT-1224-TWT-R-41276.pdf

Is the voltage of a fuse important beyond being certain it's greater than or equal to the expected voltage? Is it strictly the amperage of the fuse I should be concerned with?

you only need to be concerned with amperage really. you can get 40ma cartridge fuses... how are you going to fuse it tho? hot glue to pcb? wire off the board to somewhere?

BloodyCactus wrote:

you only need to be concerned with amperage really. you can get 40ma cartridge fuses... how are you going to fuse it tho? hot glue to pcb? wire off the board to somewhere?

Well, I already burnt the trace up previously, so I've soldered a few small pieces of wire across the back of the board. I'd simply stick a resettable fuse or a littelfuse in the circuit instead of plain wire.

I pushed some code to github for Sergey's bios

https://github.com/stu/xi8088_bios/tree/0.9.1

The 0.9.1 is a working copy, master is 0.9 from Sergey's original tar file. If he has a git/svn its not public that I can see. The .bin files are up to date.

This fixes a serial + printer port bug, updates the count of ports so things like Norton Utilities will see they exist. Bios Data Area has a count as well as port IO list, 0.9 only sets IO port list, does not set the count. I fixed that now SysInfo from NU will see correct number of ser/par ports.

Also tried to fix the FF bug in RTC, seems to be ok on mine. Also includes updated XTIDE bios etc etc etc.

I have other fixes I'm testing, but not pushed out.

Almost finished with my complete build. The Tandy 1000SL case was a nice touch but it didn't provide enough external slots, so I picked up a nice desktop case.

I'm using a Paradise EGA card, Lo-Tech CF adapter, Malinov's FDC/Serial controller, a BocaIO 4 x 2 serial/parallel card, and Soundblaster 2.0 with CMS upgrade chips (and Malinov backplane of course). I'm gathering the parts for a Lo-Tech 2MB EMS board, and actually attempting to breadboard James Pearce's repro Tandy 1000 ISA soundcard schematic for the ultimate in 80's game audio compatibility: Tandy 1000 3-voice, Creative Music System, and Soundblaster.

I've picked up a parallel port network adapter which seems to be working OK, but haven't had the time to really get it set up yet. I'm also going to grab a Roland MT-32 to compliment my "DR-Rythm 550", which is a weird rhythm accompaniment midi thing but it seems to work just fine as a General Midi device. I haven't gotten it connected yet but as I recall X-Wing sounded glorious on it.

On an unrelated note, I wonder if one of the 286 upgrade cards would work with the xi8088... I wish I had one to try out!

Im just waiting to find a 8bit floppy card. i read reports of sergey's fdc card has issues..

BloodyCactus wrote:

Im just waiting to find a 8bit floppy card. i read reports of sergey's fdc card has issues..

Hm I haven't had any issues. What kind of problems did you hear about?

i recall posts on vcfed from a couple of poeople + sergey himself with some oddities or issues.

When I bought my boards I just forgot to get the FDC pcb, and didnt want to pay shipping just for that board alone 😒 I probably should isntead of watching ebay for the right card to come along that does not cost crazy $$$$

Hm. Well I guess I have gotten lucky. I DID have some minor issues with the floppy bios not initializing when I was using it on my tandy 1000, had to have the floppy init before the XT-IDE bios, but the xi8088 bios has the floppy bios built-in so that hasn't been a problem on this system.

I think it's mostly the Trident VGA card in a 8 bit slot that has issues, in that it doesn't work on an XT at all. They never got to the bottom of it as far as I could tell.
http://www.malinov.com/Home/sergeys-projects/isa-supervga

Noticed a few odd things; using hma and upper memory blocks is freezing my system. Occasionally I receive a memory failure message during boot. Seems to work fine as long as I don't use himem.sys.

I wonder if this could be a keyboard controller error, doesn't that have something to do with HMA access?

himem.sys requires 286 CPU.

matze79 wrote:

himem.sys requires 286 CPU.

My understanding was that DR-DOS himem.sys worked fine on a v20.

In fact, it does seem to work OK for a while but then locks up, which might actually mean it ISN'T working properly...

I just use USE!UMB, hex edit the address in, and get all the upper memory the bios does not use, so I can do loadhigh etc. 96kb or 128kb upper memory, I forget.

ftp://ftp.icm.edu.pl/pub/msdos/coast/memutil/use-umbs.zip

I dont know about dr-dos himem, msdos himem did need 286+.

keenerb wrote:

Noticed a few odd things; using hma and upper memory blocks is freezing my system. Occasionally I receive a memory failure message during boot. Seems to work fine as long as I don't use himem.sys.

I wonder if this could be a keyboard controller error, doesn't that have something to do with HMA access?

the keyboard controller is used to gate the A20 on 286+ computers. the chip were using on the xi8088 supports that but we obviously dont have a 286 cpu....

Um, himem or no himem, you still can't access HMA even with a V20. Not enough address lines.

The HMA is a 286 fluke. On a 8086/8088 those addresses will roll over in the first 64k of conventional memory. Again, because of not enough address lines.

stamasd wrote:

Um, himem or no himem, you still can't access HMA even with a V20. Not enough address lines.

The HMA is a 286 fluke. On a 8086/8088 those addresses will roll over in the first 64k of conventional memory. Again, because of not enough address lines.

Yup. Some 8088 emulators do support this stuff, though. XMS could also be possible on an XT class machine.
Extended Memory, however, can't. It would either involve a different processor or a modified (hacked) 808x.
But even then, this (extra) memory had to be directly attached to the processor, because that memory is beyond the address range of the PC bus.

Jo22 wrote:

Yup. Some 8088 emulators do support this stuff, though.

Those are not accurate emulators though. To access anything above the first 1M you need address line 20. A real 8088/8086 only has physical address lines 0-19.

I got all the remaining parts for my Malinov VGA card and promptly f*cked the whole thing up by using WAAAAY too much solder on the SMD trident chip, and neglected to get it perfectly centered.

🙁

Lesson learned. I sincerely doubt I can get this sucker desoldered cleanly, I suppose I'll be ordering another board and chip...