Dear William Scott, Bill.

Thank you very much.

I can send the message after stoppage of receipt. The write function is executed normally.
Though read function is executed normally, my program can't receive any message.

I made LED message receive/transmit checker at the other MCU.

The MCU seems not to send/receive message.

This serial port hang happens after 2~3 days from program running.

Once this happens, the serial port does not work even though I re-run the program.

If I reboot or power down/up agin, the serial port works.

Thank you very much.