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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?

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  • \$\begingroup\$ here's some info from the service manual. \$\endgroup\$ – Brad Holland Sep 12 '14 at 17:19
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What you seek is a tool named logic analyzer, such as this one http://www.dx.com/p/logic-analyzer-w-dupont-lines-and-usb-cable-for-scm-black-148945

A software which goes with it should be able to decode UART as well as many other protocols to faciliate the reverse engineering.

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You can do it either Hardware or Software.

Hardware: Buy something as mentioned by Spark. Or build your own; In general use some thing like and Arduino to echo between SoftSerial (on an UNO or Serial on a Leo) to the Serial. Where you wire the SoftSerial to your 422 bus through an appropriate interface drivers.

Software: Or simpler use software to Sniffer the messages to the serial port to capture the data. On windows something like http://freeserialanalyzer.com/ looks good enough.

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You can monitoring the data RS232/422/485 COM ports and also displays, logs and analyzes all serial port activity in a system by utility https://github.com/eltima-software/RS232-Data-Logger From my firsthand experience it’s free and does all it claims to do with no restrictions.

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