I'm reverse-engineering a serial protocol and getting frustrated by bad tools. Does anyone know of a good, free tool for logging data to/from serial ports on Windows?

Requirements:

• Must be free
• Must not take control of the port (i.e. must hook the file APIs or the kernel rather than trying to open the device)
• Must have some sort of filtering features
• Writes either human-readable or binary logs, preferably in an easy to parse format

Any ideas? Portmon works, but its logs are difficult to work with and its filters are effectively useless; I've also tried a few commercial tools and nothing seems to fit the bill.

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4 Answers

I hear a lot of good things about com0com, which is a software port emulator. You can "connect" a physical serial port through it, so that your software uses the (monitored) virtual port, and forwards all traffic to/from a physical port. I haven't used it myself, but I've seen it recommended here on SO a lot.

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Portmon from sysinternals (now MSFT) is probably the best monitor.

I haven't found a good free tool that will emulate a port and record/replay comms. The commercial ones were expensive and either so limited or so complex if you want to respond to commands that I ended up using expect and python on a second machine.

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I've been down this road and eventually opted for a hardware data scope that does non-instrusive in-line monitoring. The software solutions that I tried didn't work for me. If you had a spare PC you could probably build one, albeit rather bulky. This software data scope may work, as might this, but I haven't tried either.

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I'd get a logic analyzer and wire it up to the serial port. I think there are probably only two lines you need (Tx/Rx), so there should be plenty of cheap logic analyzers available. You don't have a clock line handy though, so that could get tricky.

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