When configuring the COM port to MODBUS the break signal switches the com port to RS232 PCOM and then you are unable to communicate with the PLC.
There is a system bit that turns on when break signal occurs SB 330,331, and 332 for COM port 1, 2, and 3 respectively. You can use this system bit to change the com port setting to RS485 again (since the break signal changes it to RS232 by default).
As you can see in the attached application after the SB 331 for COM 2 rises, we wait 5 seconds and change the com port settings to RS485. The disadvantage of this workaround is that you will need to try establishing the communication 2 times, the first time will change the com port to RS485 but you will receive error message that there is no communication but in the second time you will be able already to communicate. We tested it here using direct connection and also by network ID and it works properly.
For customers that wish to re-establish communications afterwards with the original protocol SB 133 and 136, data transmit and receive can be used to power a timer when not active. After a pre-determined length of time this can re-initialize Modbus communications.