@RyanFikri (1) Ah, the original wiring diagram you posted is already the full duplex mode, ie, TxD is used to send instruction packets, and RxD are use to receive status packets. (2) For half duplex, only TxD is used, RxD is NOT used，ie, only send, no receive. (3) You can use any python loopback program to send and receive, just disconnect the jumper wire shorting TxD and RxD. Instead TxD and RxD connected to the AX-12A.