Hi Corinna,
the best way would be to connect any device on serial port which
utilizes both one of output lines(DTR and RTS) and one of input lines
(DSR, CTS, RI,CD) and test it. I do a lot of work with smart card
readers. One of models utilize RTS and CTS line. I tested my patch this
way ( converting my existing Windows reader driver to Cygwin driver)
seting in needed moments RTS line and reading CTS line. All of course by
ioctl() function. I realize You may not have such device but if You have
in Your company any person who is able to prepare D-SUB9 or D-SUB25
female connector( making loops between inputs and outputs) and connect
it to Your male PC serial connector, You will be able to set requested
output lines states and read them by input lines.
In other words, a serial loopback plug, which should be the part of any
respectable computer technician's toolkit [very useful for verifying the
integrity of serial ports]. I'm sure the one who works for your RedHat
branch should have one. Jacek, shouldn't it also be possible to port
minicom and use that in conjunction with a modem to see if the signals
are being sent and recieved?