BArry thanks for the help. I've also come over the things you mention in the post over the last days. True, the RFX9600 serial extender uses only the TX, RX and GND pins, no others. But the MArantz needs an external device to set a line to which it listens so it gets ready to recieve the data. Unfortunatelly the RFX9600 isn't capable of setting that line.

To make things more complicated, the MArants in itself too doesent use all of the rs232 pins but only Tx, Rx, CTS, RTS and GND. So there is no DCD or DSR pins used, so i can't use them to provide the necessary RTS.

I will soon start working on a small interface which transforms philips's 3 pin communication to a 5 pin communication with the flow control. Currently i'm looking for a small footprint microcontroller that will have all the necessary periphery.

Anyway, thank you very much for your help.

Edit, i found something new. Seems that Marantz implemented an older version of the rs232 protocol, which goes like this:

Old RTS/CTS handshaking is different

What is confusing is that there is the original use of RTS where it means about the opposite of the previous explanation above. This original meaning is: I Request To Send to you. This request was intended to be sent from a terminal (or computer) to a modem which, if it decided to grant the request, would send back an asserted CTS from its CTS pin to the CTS pin of the computer: You are Cleared To Send to me. Note that in contrast to the modern RTS/CTS bi-directional flow control, this only protects the flow in one direction: from the computer (or terminal) to the modem.

For older terminals, RTS may have this meaning and goes high when the terminal has data to send out. The above use is a form of flow control since if the modem wants the computer to stop sending it drops CTS (connected to CTS at the computer) and the computer stops sending.

Which is the opposite of the modern Flow control. Strange decisions were made during the development of the device.