Serial communication Watlow F4, Timeout error

Hi guys,

I am trying to set up a communication between Matlab and a Watlow F4 controller assigned to a Arbin temperature chamber at the moment.

The communication between Matlab and the Watlow is via Modbus. The Watlow has an RS232 connector, via an RS232 to USB adapter the controller is connected to the PC.

What I am doing so far:

    s = serial('COM5');    % Port the controller is connected to
    fopen(s);              % works, the port is open after that
    fprintf(s, 'r103');    % 103 is the register to get the status of the power output, due to the user manual
    out = fscanf(s);

The answer on that is a timeout error: 'A Timeout occurred before the Terminator was reached.'

I tried to change different parameters (BaudRate, TimeOut, Terminator, FlowControl, ...) and tried different registers for fprintf but the error still appears.

My questions:

• Is my approach to fast, do I need to use any drivers for the Modbus or do I need to setup anything for the communication before I can open/use the port? (Am I thinking to easy in this way?)
• Or is this way correct and I got maybe different problems?
• Can anyone tell me the correct properties for BaudRate, Terminator, ... for a Modbus communication to the Watlow F4?

EDIT: I tried to communicate with the Watlow with an extra software (Modbus Scanner from Chipkin), but still got always timeout errors. So this sounds like the problem is not really the communication via Matlab but the communication with the controller in general?