Problem interfacing RF modem through USB port in Linux

[ponnus]

Hai,
Pardon me if this is not the right forum to ask this question.

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....

Thanks

[larrythethird`]

A lot of modems need to be initialized for them to work. I don't know about this modem in particular, but the old Hayes compatible modems needed a string of commands to "wake up". You had to set the baud rate and you could change the port rates amongst other things. I would imagine this modem is no different. Look through the manual to find the init string.

[ponnus]

Hai,
Thanks for your reply.........
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.
Thanks

[larrythethird`]

It would have to be the hardware setup either in RHEL6 or the BIOS. It's probably in RHEL6, I would suspect. The BIOS usually sets comm ports at 9600. That was the old standard. 115200 is the top speed the port can be set to. Check in the system settings. It has to be something in a /dev/tty? or /dev/stty? setting somewhere.

[ponnus]

Hai,
I am not able to open /dev/tty using gedit.

But, even if the default baudrate is 115200, the system should send at 9600 as i've set it so.
Anyway, after configuring that IC for 9600 baudrate, the system is sending at 9600.

Thank you for your response