Considering the board:
It seems to use the MCU (microcontroller) to receive and send the answer, so the activation of en-RX and en-TX is done by software on the pic....
This make it idfficult, because writing a MCU just for that is an big task.
I am looking now to create a timer circuit with a 555, detecting the first "low" bit of the communication and setting en-TX for the time of transmission of one byte. I ordered the 555, but is not yet here (probably tomorrow or Wed).