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BGS5T serial communication issues | Telit Cinterion IoT Developer Community

January 20, 2015 - 12:26am, 10768 views


I've written TCP/IP to serial modbus protocol 'gateway' for BGS5T module, but cannot get it completelly working due to serial communication. My setup:

BGS5T modem, power saving disabled, Userware/Stdout set to null, using this connection string:

"comm:COM0;baudrate=9600;parity=none;blocking=off;autocts=off;autorts=off" (tried many other variants as well, including stopbits, databits, ... etc.)


- BGS5 connected trough serial<-> usb converter cable to pc;

- Modbus simulator runs on the pc, opened serial port for communication, I have some simulated data entered in it

Result: everything's just fine. I can get those simulated values from serial port and send it back as a modbus TCP response to connected client via BGS5.

2) I have two different PLCs (twido and unitronics jazz). If I connect those directly to the same rs232<->usb cable to the same PC (same rs232 params as defined above in connection string) on serial port and scan the values from them (using 03 modbus function etc.) everyting's also just fine.  

Now important part: both PLCs are DCE devices (have female serial port/cable) also the BGS5T is DCE/female device. So, connecting BGS5 to PLC requires "gender changer" / null modem converter. I have original converter especially used for that, and also bought DB9:male<=>DB9:male cable.

Problem: Whatever I use, I cannot get any PLC to respond to serial data sent to it. I am 100% guaranteed that data is sent (connected to terminal and got the exact HEX values I am expecting). Tried male/male converter, cable, also I've cut and rewired the cable Rx/Tx (made it crossed). Nothing works.

Question: Are there any rules I should fulfill using serial port (RTS/DTS signals etc.), or maybe you have any insights/suggestions. Any special wiring must be fullfilled (f.e. null modem cannot be used for some reasons)? I would really appreciate it. It's 3rd day I cannot sleep anymore... :)