Electronic – arduino – Reverse engineering old serial devices and cloning with Arduino

I have a piece of music equipment that uses a remote control. This remote control communicates bi-directionally with the main unit. It communicates over RS-422 protocol (mainly for the cable distance, I believe).

I have purchased a couple of RS422 to USB adapters with the intention of snooping the data in both directions using some serial port monitoring software.

I haven't quite gotten that to work properly on its own yet; I think it's most likely the connection settings I am attempting as the data I see looks messed up. From what I can tell from the service manual, this should be 8 bit characters with no parity and 2 stop bits.

Anyway, as this device is now archaic in terms of technology (1982, I believe), I think it would be a great candidate for cloning with an Arduino.

The remote itself uses an old Intel 8749 microcontroller. This was an MCS-48 based device (I think) which also had a small EEPROM built into it for program memory. This was 8-bit with 3 I/O ports.

The remote unit basically has 12 old Litronics DL-1414 alphanumeric 4 digit displays (which receive an ASCII character and hold it in their memory until refreshed), a bank of buttons and faders (which are connected via an ADC) and a dB level meter.

I have the service manual of the unit which goes into much more depth about the bit addressing scheme of the devices, which I can upload.

I might be thinking about this the wrong way but my idea was to sniff and capture the data being sent and received to figure out what is sent, when for instance, a fader is moved. This I would imagine would then be easy to strap to a slide pot in Arduino and then have that movement sent to the serial bus possibly with some control bits added and then the value.

I'd really appreciate some thoughts and maybe advice, on how such reverse engineering can be tackled?