Hallo Bartosz,

the RS-232 standard is the most violated and abused standard ever invented!
RS-232 standard does only define ONE connection: A DTE to a DCE. All other possible connections of DTEs and DCEs intermixed together are not defined by the standard!

A DTE is a Data Terminal Equipement, for instance your microcontroller board, and a DCE is a Data Communication Equipement, for instance a modem. It was never assumed by the standard, that two DTEs are directly connected without inserting two DCEs. So, a connection, which complies to the standard would be: DTE-DCE-link-DCE-DTE. A DTE-DTE connection was never taken into consideration! That's where all the trouble comes from. And it's clear, that by this misconnection now the other signals like RTS, CTS, DTR, DSR and DCD can become a total different meaning...

By the way: Standard also defines a DTE connector to be 'male' and a DCE connector to be 'female'. This norm is also widely violated.

To me it seems to be the best to avoid all these additional handshaking lines, if possible, and to use a clever software handshaking protocol, instead. Then everything that has to be connected is TxD, RxD and GND.

Kai