FXT009 RS232 communication freezing


I have problem with communication over RS232.

Modem is used to sending SMS messages, approx 5 per day.

Modem has factory settings, just echo is switched off.

Sometimes modem simply stops to communicate.

This happen sometimes after 3 weeks and sometimes after 2 days.

When serial link stops to communicate, i dont get response to any AT command.

And i have to restart modem(cycle power).

I tried several firmwares, but without succes.

Does anybody have similar problem or idea how to solve it?


When the modem gets stuck, are you able to communicate using USB or is it not responding with USB also?
What exactly the modem is doing apart from sending sms? is it in field?. seems to be really strange behavior.
using USB for a longer period of time instead of UART causes issues??

What is controlling the modem - Open-AT application, or external host?

If it’s an external host, is it being careful to wait for each command to complete before it sends the next…?