Matlab Serial RS232 connection with a null modem not working

I am using the serial function in matlab to control a device that uses a standard RS232 cable and this works fine. When I try and control another device which needs a null modem cable I run into problems.

I have set the parameters like BaudRate, Parity, Terminator etc. to match that of the device. When i use PuTTY to control the device I have no problems. When I use the matlab serial function it does not work. Matlab turns some of the flowcontrol pins on when it is not supposed to. The following pins are active when using different flowcontrol settings:

Matlab

Flowcontrol: None RTS: ON, CTS: ON, DSR: OFF, DCD: OFF, DTR: ON, RI: OFF

Flowcontrol: Hardware RTS: ON, CTS: ON, DSR: OFF, DCD: OFF, DTR: ON, RI: OFF

Flowcontrol: Software RTS: ON, CTS: ON, DSR: OFF, DCD: OFF, DTR: ON, RI: OFF

PuttY

Flowcontrol: None RTS: ON, CTS: Neutral, DSR: Neutral, DCD: Neutral, DTR: ON, RI: Neutral

Flowcontrol: Hardware RTS: Neutral, CTS: Neutral, DSR: Neutral, DCD: Neutral, DTR: ON, RI: Neutral

Flowcontrol: Software RTS: ON, CTS: Neutral, DSR: Neutral, DCD: Neutral, DTR: ON, RI: Neutral

 With PuTTY it always goes well but in matlab it only rarely gives the correct response. What causes Matlab to behave this way?

Example of my code:

s = serial('COM1','Parity','even','DataBits',7,'Baudrate',19200,'StopBits',1,'FlowControl','hardware','Terminator',{'CR/LF','CR'});
            fopen(s);
            fprintf(s,'ID?');
            fscanf(s)
fwrite(s,'['ID?' 13 10])
fscanf(s)

Answer 1

[Vinod]

Depending on your hardware requirements, you may need to unassert the RTS and DTR pins during the opening of the serial object.

s = serial('COM1','Parity','even','DataBits',7,'Baudrate',19200,'StopBits',1,'FlowControl','none','Terminator',{'CR/LF','CR'}, 'RequestToSend', 'off', 'DataTerminalReady','off');

See more information here:

https://www.mathworks.com/help/matlab/matlab_external/dataterminalready.html https://www.mathworks.com/help/matlab/matlab_external/requesttosend.html