Reverse Engineering old serial devices and cloning with arduino.

Question

I guess this is a strange topic and might not be one anyone here could give any advice on but here goes...

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 adaptors with the intention of snooping the data in both directions using some serial port monitoring software.

I havent quite gotten that to work properly on its own yet I think its 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.

Anyways, 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 eprom 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 recieve an ascii character and hold it in their memory until refreshed), a bank of buttons and faders (which are conected 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 recieved 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...

Thanks in advance,

Brad

michaelkellett · Answer

USB adapters aren't the best way to do this (but might be your only choice). A logic analyser or better still a scope and a logic analyser (built in or separate) are the ideal tools. You can use the scope to check baud rate, data bits and parity etc that is actually used (never trust a manual 100%) and the packet structure of the data.. The logic analyser needs to be able to decode the serial stream and then you can look at the actual data in the packets. There are some very cheap logic analysers on the market that will do the job. If you are stuck with your 422->USB converters then make sure they are set up for least possible buffering and quickest response (otherwise they may mess up the packet structure). What software are you using to look at the data - it is quite unlikely to be ascii coded. MK

michaelkellett · Answer

The problem you have is that the Arduino serial ports work at 5V logic level and a PC will probably only have USB. So you end up needing different [RS422 -> something] converters. USB to serial adapters can often add their own issues. Since you already have the RS422 -> USB converters we may as well start with them: You need to get your scope on the RS422 wires so you can sort out what's going on. What make/model are the RS422 converters, what software are you running on the PC to talk to them (if at all possible please try using Hyperterminal - it's much simpler than many of the alternatives and so easier to debug.) Do the two RS422 adapters appear as different COM ports ? The basic plan is to use your scope to look at signals on RS422 being sent from the PC first - then we know what the PC expects to receive. Then you can check the signals from the remote and make sure that they are the same format and polarity as the PC is sending out. At this point it ought to work. MK

Reverse Engineering old serial devices and cloning with arduino.

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