Benji Lister wrote:

Firstly, kudos to the Dosbox programmers for creating this useful software.

Support for non-game applications is limited, just so you know.

So just out of curiousity, can someone explain what Dosbox is doing that fixes the problem?

That would depend entirely on just what "the problem" is, exactly.

Support for non-game applications is limited, just so you know.

Yes, I had noticed the prudent disclaimer thread 😉

That would depend entirely on just what "the problem" is, exactly.

The original problem was that the PLC's programming software could never establish comms with the PLC via a serial link. A breakout box in between them showed an initial brief TX signal out, a brief RX signal back to the PC, and shortly after the program would complain of "comms timeout, check settings".

The problem never occurred with a previous laptop, which was identical except its OS was Win98 instead of XP. I'm guessing XP handles serial comms differently to 98, which Dosbox is "undoing"?

Accessing parallel ports can be tricky in Windows 2000/XP/Vista/7, but I don't think there's any particular restriction on serial ports. Or maybe there is? See http://retired.beyondlogic.org/porttalk/porttalk.htm . (See also UserPort.)

Since you say the application is speed-sensitive, it could be that your Windows 98 computer was slow enough for the program to work correctly, while your Windows XP computer is too fast. Or do you mean the two laptops had identical hardware?

The best way to be sure would be to simply use a DOS boot disk of some sort in your XP computer and see if you have problems running the program straight from DOS.

Jorpho wrote:

Since you say the application is speed-sensitive, it could be that your Windows 98 computer was slow enough for the program to work correctly, while your Windows XP computer is too fast. Or do you mean the two laptops had identical hardware?

I'd say that's probably it. Seems that many apps for programming PROMs/PLCs over serial are really rather speed sensitive, and tailored for machines of the period when they were written - OS and all notwithstanding.