dosbox_agent - I hope every programmer is happy to receive error reports about their program, and I hope that includes the people behind DOSBox too. But you also have to remember what the primary purpose of DOSBox is: To play games.
The modem/serial port support that is built into the standard DOSBox release is there to allow 2 or more computers to be connected for multi-player games. And for that it seems to work okay.
h-a-l-9000 improved on the serial-port support his own builds. It is not perfect, but it seems to work for some people, including people using his builds to control Motorola radios and car ignition/tuning devices.
Debugging the serial port is difficult, because it involves hardware. A software problem can usually be debugged by sending a copy of the program to one of the developers, and he/she can then try to see what the problem is. Sending a piece of hardware to a developer is a little more difficult 😀
Maybe if you can tell h-a-l-9000 more about which programs you have tried, which hardware you tried it on, etc, etc, then he can advise you on what to do. Maybe the first step is to find something that works? I don't know what to suggest. Perhaps a null-modem cable and some communication software (ProComm, X-modem, ...) to verify that the cable and the serial port is working?
DOSBox 60 seconds guide | How to ask questions
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