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Author Topic: EXDOS (Read 1698 times)

Offline Saint

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EXDOS
« on: 2014.February.09. 19:24:43 »
I've just been getting my old EXDOS board working. I found the EPROM had stopped working (it gave different results on every read!), but I didn't have any 27128 EPROMs around, but did have some 27256, so I thought about adding the extra address line for A14 and installing EXDOS 1.3. Then I noticed the PCB already has jumpers for A14 on the board! So soldered the pin 27 jumper to A14 from 5v and put in EXDOS 1.3, but it still wouldn't boot... :roll: I got all sorts of weird crashes (green screen, black screen, corrupted screen, reset), and on the rare occasion it made it to BASIC, :help showed no EXDOS.

So I thought maybe the Enterprise was the problem (this was my Arabic Enterprise), so I tried it on my original UK Enterprise, and to my surprise it boots to BASIC and :help shows EXDOS 1.3! :ds_icon_cheesygrin:

I've not replaced all the caps on the Arabic motherboard -- I'm guessing this is going to be the cause of the problem. But in-case anyone else (Zozo :lol:) knows any other reasons why this could be happening, I thought I would ask!

I have EXDOS working again!! Now I just need to dig out a floppy drive and try and write some floppies... then maybe get the HxC... :mrgreen:
« Last Edit: 2014.February.09. 19:45:02 by Saint »

Offline Saint

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Re: EXDOS
« Reply #1 on: 2014.February.09. 22:13:18 »
Taking of exdos, what is i/o port 18? 10-13 are the registers of the wd1770 which I know well from the Atari ST, but I don't see any other chips on the pcb which this relates to??

Offline Zozosoft

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Re: EXDOS
« Reply #2 on: 2014.February.09. 22:53:42 »
Quote from: Saint
Taking of exdos, what is i/o port 18? 10-13 are the registers of the wd1770 which I know well from the Atari ST, but I don't see any other chips on the pcb which this relates to??
It is outputing Drive and Side Select,In Use and Disk Change Reset signals, and reading the Ready, Disk Change and DRQ, INTRQ signals.
Chips are 74LS273, 74LS126.

Offline Zozosoft

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Re: EXDOS
« Reply #3 on: 2014.February.09. 23:01:57 »
Quote from: Saint
I've just been getting my old EXDOS board working. I found the EPROM had stopped working (it gave different results on every read!),
Do you tried to erase and reprogram it?

Quote
But in-case anyone else (Zozo :lol:) knows any other reasons why this could be happening, I thought I would ask!
Firstly try to put to the card another program than the EXDOS, for example the BASIC ROM.
If it is working then the problem with accessing the disk hardware. If no then problem with the ROM accessing.
Another idea: remove EXDOS ROM from the card and put to the cartridge and see what happen.

Offline Saint

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Re: EXDOS
« Reply #4 on: 2014.February.09. 23:10:32 »
Actually looking at the schematics it must be the 74LS126, so port 18 is..

D0, ready
D1, intrq
D6, disk change
D7, drq

The rest of the data lines appear to be floating.

Please correct me if I am wrong.

I have other random ideas in my head about emulating the wd1770 using a pic chip and CPLD bridge... Until I get some time to 'do', I do a lot of thinking... :)

Edit: posted before I read Zozo's post, thanks for the info on the output side, I hadn't spotted that yet. Makes perfect sense, the sound chip is used on the ST for drive select.

Offline Saint

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Re: EXDOS
« Reply #5 on: 2014.February.09. 23:24:21 »
Do you tried to erase and reprogram it?
Firstly try to put to the card another program than the EXDOS, for example the BASIC ROM.
If it is working then the problem with accessing the disk hardware. If no then problem with the ROM accessing.
Another idea: remove EXDOS ROM from the card and put to the cartridge and see what happen.

No, I didn't trust the ROM. If every time you read, it returns something different, it's very broken... :)

If I remove the ROM, it boots ok on the Arabic machine, so the board isn't directly causing problems. So it appears access to the ROM is getting corrupted in my opinion. It's the sort of weird behaviour I would expect from failed caps -- I actually replaced the larger cap in the EXDOS board, but I have a feeling it's all the caps I didn't replace on the EP PCB which is actually causing the problem!

Offline jltursan

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Re: EXDOS
« Reply #6 on: 2014.February.10. 20:35:46 »
Looks suspiciously like my own problem:, take a look here. Do you remember?

I also replaced all the caps of my Arabic EP64, the bridge one and finally get success by replacing the 27256 in the EXDOS card. I simply used a 150ns one.
Sooner or later I'll mount a socket adapter to use a 28C256, a lot easier to work with.

Edit: corrected a stupid typo with tags...
« Last Edit: 2014.February.28. 21:10:10 by jltursan »

Offline Zozosoft

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Re: EXDOS
« Reply #7 on: 2014.February.12. 22:51:36 »
Quote from: jltursan
finally get success by replacing the 27256 in the EXDOS card. I simply used a 150ns one.
It is interesting, probably some older(?) motherboards have a slower Dave?