Ancient PC Hardware (apparently) - aka I Need a 386 for Work

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Ancient PC Hardware (apparently) - aka I Need a 386 for Work

Postby evilspoons » Mon Sep 19, 2011 6:57 pm UTC

So I've got a job at work now to restore to working condition a 1992-era motion-controlled machine, hooked to a PC to feed in parameters. Unfortunately, the 386 SX 16 running it seems to have died of old age after sitting in storage for two years.

The 386's been replaced by the owners of the machine with an Athlon 64 4200+ with Windows XP, and the DOS program originally compiled in Turbo C actually still runs. However, it doesn't actually function properly. It's supposed to send serial commands (ASCII text commands) out on COM1 at 9600 bps and receive replies, then interpret the replies into helpful status messages and the like. It's sending the commands because I can read them in on my laptop by hooking it up via a null modem cable, and the commands are valid because I can type them by hand from my laptop into the machine and it sends values back.

The program is the same one as in 1995, the machine is the same as it was in 1995, so the only obvious change is the PC. I tried booting the new machine on the old computer's DOS boot disk, but that didn't fly for whatever reason. I created a new boot disk out of something derived from Windows 98 (DOS 7.x?) and the machine booted and ran the program, but it just failed to work in a slightly different way (incorrect values returned instead of no values returned).

So I spent all morning phoning around town (Edmonton, AB) hoping someone would have a 386 I could buy off them. No dice. Don't really want to go the eBay route because fast shipping will cost too much and nearly everything with appropriate hardware specs is being billed as "vintage" now and being sold for hundreds of dollars(!). Am I really that old? I'm only 26! This is the stuff I played with as a kid!

Any thoughts?
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Re: Ancient PC Hardware (apparently) - aka I Need a 386 for

Postby Carnildo » Tue Sep 20, 2011 4:26 am UTC

Unless the program relies on CPU speed for timing (by the 386 era, this was uncommon), you can probably get by with any 386, 486, or early Pentium. If it does rely on timing, you can try running it in DOSBox and adjusting the emulation speed until things work right.
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Re: Ancient PC Hardware (apparently) - aka I Need a 386 for

Postby cerbie » Sun Oct 09, 2011 4:37 am UTC

Might be way off, but maybe it needs +12V or +15V for the serial?

While you do pay a premium, 386 and the like computers are available on eBay all day long, if you want the real thing.
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Re: Ancient PC Hardware (apparently) - aka I Need a 386 for

Postby mbrigdan » Mon Oct 10, 2011 6:51 pm UTC

Wait, so if you connect the computer to your laptop, you see it sending valid commands, and if you send those commands using your laptop, you get the correct values, and it only fails when you connect the computer directly to the device? Maybe its little vs big-endian weirdness or something? Does that affect serial ports?
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Re: Ancient PC Hardware (apparently) - aka I Need a 386 for

Postby Tomlidich » Mon Oct 10, 2011 7:42 pm UTC

it may just be that after all these years the hardware itself has failed.
we are talking about a computer as old as I am.

i played with a 386 a bit as a kid as well.

is it absolutely necessary that it run on this antique, or is it just some corporate schmuck trying to squeeze pennies?

you could try the virtual machine route as well and just run the dos on that.
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Re: Ancient PC Hardware (apparently) - aka I Need a 386 for

Postby mosc » Mon Oct 10, 2011 8:46 pm UTC

You need a CPU that you can install dos on and not emulation. What you're talking about is hardware level code manually programming the serial port. They don't allow that stuff anymore. You need a P3 or older computer fortunately, doesn't have to be a 386. P4's don't run dos natively very well and I don't think anything newer than that (like the athlon you're talking about) can run it at all. I'd get yourself a nice copy of windows 98 SE to go along with it. It's dos under the hood and still allows direct control of serial ports.
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Re: Ancient PC Hardware (apparently) - aka I Need a 386 for

Postby BrianB » Wed Nov 30, 2011 10:11 pm UTC

One problem could be that the serial port in Windows is set for HW flow control.

Go to "Start Menu" -> "Settings" -> "Control Panel" -> "System" -> "Hardware" -> "Device Manager" -> "Ports" -> "Com1" -> "Port Settings" and set "Flow Control" to "None" and hit "OK".

You may also need to run the old program in "Compatibility Mode", though I think not since you already can send to the laptop ok, and the laptop can talk to the machine ok.

Your most likely problem (given the info you posted already) was already mentioned - voltage levels. Newer PCs use RS-232 transceivers that "charge-pump" from 3.3V to get about 6 to 7 volt signal levels on the external port. This is close to the minimum input requirement of old equipment based on older RS-232 specifications (e.g. RS-232C).

In this last case - you might look at adding an RS-232 Repeater, like these at B&B Electronics

One of these should solve your problem.
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