comaxs.exe COM11 10 FE FE 00 E0 03 FD
will write the sequence (fe fe 00 e0 03 fd) to COM11 and then listen until 16 (0x10 bytes are received.
In PHP you can call the tool like:
$x=shell_exec("g:/c/comxs.exe $comport $readbytes $command");
$x will contain (as a written string):
"fe fe 00 e0 03 fd fe fe e0 00 03 66 10 20 14 00 fd"
(This is a CI-V dialogue for the Perseus SDR communications receiver)
Download comaxs.zip
It's very basic and still beta. There is no timeout - the process will be active until the requested number of bytes have been received. Use 0 for write-only. If you want a more stable and elegant solution take a look at phpser.dll by TheByteWorks (with delays in the trial version).
This site is based at: radiovibrations.com/php/com-port-access.htm