Differential signal processing and generation
That is almost certainly an RS485 signal. It's a very robust differential protocol used a lot in industrial settings.

RS485 is just a signalling standard, there is no protocol. Typically standard UART protocols are used. Because of this a standard PC RS232 connection, through an RS232 to RS485 level converter is all that's needed to connect to the device.

I recommend purchasing something like this: http://www.amazon.com/RS232-To-RS485-Converter-Adapter/dp/B003MN1KKQ and testing the output to confirm that it is giving you UART type signaling. 

You should be able to bring the RS232 level signal into a PC and view the result in a terminal. I love realterm for this, because it has a good "hex mode" which helps you confirm that there is real data there, even if the protocol is binary and not ASCII text.

If all goes well, and you can confirm that you are dealing with RS485 there are plenty of RS485 to LVTTL level chips that will interface cleanly to your microcontroller pins.

If you really need to use an opamp for this, a standard subtractive circuit will do the trick:







simulate this circuit &ndash; Schematic created using CircuitLab