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IMB PC/XT in a lab equipment

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Benius

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Nov 18, 2011
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Hello,

I'm currently trying to upgrade an old lab equipment. It is a TLD reader (a device used in hospital ant physics labs for reading radiation doses). It uses an XT with a proprietary card to control the mechanics and the reader itself, does all the counting etc. The board itself is a 2x8255/8254 card with extra bits.
The device was not working, so got a new motherboard. Right now I want to replace the whole XT system with something that has an USB port, since the only way to get the data out of the device right now is the 5.25 floppies.
I've tried putting the proprietary card into a newest pc that I could get my hands on that had an ISA slot (Celeron 1.3GHz), but it seems to have damaged the card. So I replaced both 8255 chips, and it is working, back on it's XT system. So I was wondering what could be the problem, why the card got damaged. Can it be that the card uses CPU clock as it's own clock? Or the card could be not compatible with the 16bit ISA?
I have all the schematics of the device, and building a new card that is compatible with a newer CPU or 16bit ISA is not a problem :)
I would really appreciate any ideas :)
There will be quite some work involved in placing an atx board in an XT place. The power supply to has a lot of proprietary connections for the reader, so a new one will have to be modified. I will upload more info as it goes along, if someone will be interested :)

Thank you,
Benius

Edit: This is the service manual for the machine:
http://www.failai.lt/yppe3e4r9bw8/service.pdf.htm
 
Last edited:
Hello, and welcome 8)

Please do post some more info on this..., is this an original IBM XT, c.1984, still in use in some kind of real environment?
 
No. The board that is in right now is the same as the original (pulled from another same device that has other hardware bits failed). It is 1986 XT compatible system. And yes, the machine that I am currently trying to mod was pretty much used monthly till a couple of months ago, "build like a tank" :)
 
This looks like an ambitious project.

I doubt that the new system was responsible for the failure of the ISA card--you're dealing with old components and sometimes simply moving things around causes failures.

The thing to think about, however, is that your newer Celeron system may turn out to be less reliable than your XT. In the XT, the technology is conservatve, though-hole mount and low power (compared to a Celeron.

It may not make a difference, but many systems with chipsets later than the Intel 440BX with ISA slots often make compromises in ISA compatibility. For example, I have a couple of later systems that have ISA slots, but do not implement ISA DMA.

Another thing to be aware of is that CPU timing loops were common in old 8088-era equipment. Putting this on a faster CPU may cause that code to stop functioning.

All in all, if you're determined to move forward, you may want to consider something such as Valentin's Flea86 system, which now includes some ISA support. It may actually be a better match to your needs than a more modern commodity PC.
 
Thanks for your input :)

Flea86 seems to be a really cool project, but using this kind of hardware is a bit out of my league. The main reason why I want to mod this system is to get it to a state that all of its pc components would be somewhat readily available. The floppy to usb devices discussed on other thread would solve the getting data on/of the device, but the HDD will fail at some point (ST-238), and if there will be some other problems with other XT hardware, it is quite hard to get, since I'm from Lithuania, and at the time the XT systems were at their peak, here there were some russian clones which are even harder to get these days. And the newer system would allow modern OS to be used.

I was thinking, can't the card get damaged because there is another device in the system that uses the same port range. Since, IF I understand correctly, the 8255 cards create a range of ports, that can be configured for specific tasks. If another device in the system is using the same port range as the card the 8255 might get shorted of something like that. There is no way to change the port range on the card as far as I can tell. Can this be the case?
 
Labas! Nice to hear from someone from the "old country"--my grandparents emigrated from Lithuania nearly 100 years ago.

I have never seen the case of two cards sharing the same I/O port or address space doing damage. The bus interface drivers are usually quite robust (consult the data sheets) and long before something gets damaged, one notices that the system doesn't operate in the expected way.

Inserting a card in a running machine is a different matter (the ISA bus was not designed for hot-swapping) and inserting a card such that the contacts are misaligned or crossed is a different matter and may cause damage.

Let's talk realities, however.

The early PCs were made to be repaired. There is no shortage of parts to repair them, not even in Lithuania, if my browsing of the evita.lt site is any indication. On the other hand, recent PC components were made to be discarded when they fail. As evidence, try to find replacements for the LSI components of that 1.3GHz Celeron board that you're looking at. While it's true that newer PCs are faster, it's also true that this is an application that cannot make use of the 1000-fold increase in speed offered by newer designs.

As seen by the XTIDE project here, replacements for your hard disk can be engineered. In fact, there are competing designs.

If I were in your position, I would analyze my needs--how long will this equipment continue to be useful? Will 20 years be sufficient? If that's the case, I would lay in a hoard of components for servicing the old equipment (PC XT "clones" must still exist in your area--the Soviets made quite a number of them) and continue to make use of your current setup.

We have a saying here, "If it ain't broke, don't fix it". I think that applies in this case.
 
If you do stick with the XT, there are several ways you could make the data transfer more convenient.

Logomatic- plug it into the serial port, dump your data to serial, and it writes it to an SD card. Or just nullmodem the serial to another computer.

You can also find 8bit network cards.
 
That's a perfect application for InterLink...... go serial to serial into a newer computer with a USB port. Win98 should work like a charm.
 
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