Real Time Windows Target doesn't set the serial port configuration

Hello,

iam using Matlab R2012a with Real Time Windows Target 4.0 to read and write data to a device connected over RS-232 (Serial Port). It works fine using my m-File (see below) or the Matlab Terminal but not with my Simulink + RTWT model. I installed a standard serial port (Install new Board) and configured the port with the board setup as required. (COM1, 2400 baud, 8 databits, 2 stopbits, none parity, DTR off and RTS on). Screenshots below. After some hours spending on troubleshooting I measured the voltage of each RS-232 pin using the (working) m-File and for comparison the (not working) model. It differs in the DTR and RTS. My m-File sets these pins on the right voltage (DTR -12V, RTS +12V), the model (DTR and RTS +12V) not. Then I tried different combinations of RTS, DTS, XOn on/off...and measured the voltage every time but the voltagelevel stays the same. At this point I dont know what to do next. Does someone have a good idea?

m-File:

    s = serial('COM1','BaudRate',2400,'DataBits',8,'StopBits',2,'Parity','None','DataTerminalReady','off','RequestToSend','on','Terminator','LF');
fopen(s); %and so on

Thank you!

kind regards, Jonas