Problem interfacing RF modem through USB port in Linux

I’m working on RHEL6 Linux platform. I’ve a 24Xstream RF modem. I’ve interfaced it with linux usb port and able to communicate with the modem.

I’ve written a program to receive data from another RF modem. Also, added the linux user to the group dialout, so that the program has the permission to access usb port ttyUSB0.

Everything is working fine and the RF modem is receiving correct data…except for the first time…i.e,When I connect the modem to the port for the first time and run the program, the modem is responding to all AT commands. But it receives only ‘zeros’ from the other RF module…

But,if I send a command to the modem through terminal and then again run the program,…it is reciving correct data from the other RF modem…



My problem is solved. I’ve checked the signalling of uart.
I was setting 9600 baudrate for uart, but when I connect the modem for the first time, my program was sending data at 115200 baud rate. I don’t why this happens?

The modem has an IC to convert the usb data to serial data. I’ve configured the baudrate of the IC to 9600. So, at whatever baudrate the system tries to communicate with the modem, the IC converts it to 9600 baud rate. Now it is working from my program…

But still ,I don’t understand, why the system sends at 115200 baudrate, even if I set uart at 9600.