The common layout for the TRS serial cables that I've seen are:
- Tip - Receive
- Ring - Transmit
- Sleeve - Ground
_
\_/ <- Rx
| | <- Tx
|_|
| | <- Ground
|_|
If you have a TRRS connection, typically the sleve and the lower ring are both ground.
However there's no guarantee this is going to be correct for your specific device (I've no idea what a MZC 64 is). Good news is that you're unlikely to mess anything up seriously, so some trial and error might be the way to go.
I would also suggest asking over on our electrical engineering site. It may not be as simple as just wiring it straight up, there might be TTL logic or level shifting or something else required that's baked into the OEM cable.