Most geophysical gear I run across is SDI12, or at least SDI12 as an option alongside others such as RS485 or RS232 proper. SDI12, for those who don't know, is a standard per http://www.sdi-12.org/. It can chain multiple geophysical devices along a 3-wire cable, ground, power and bidirectional data. Communication is at 1200 baud, 5 volt levels (active low, pullup high) using RS232 ascii codes. Each device has an address and responds only when spoken to.
As a "general purpose" device I'd imagine that most everything related to the measurement and processing would be taken care of by the core processor based on commands over the main interface The cable to the outside would only need 4 lines max, maybe 5 if you include an external GPS trigger.
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BTW, just because I say don't use RS232 that doesn't mean you can't connect to it and be compatible with it, just as 0-5V GPS units do.
As a "general purpose" device I'd imagine that most everything related to the measurement and processing would be taken care of by the core processor based on commands over the main interface The cable to the outside would only need 4 lines max, maybe 5 if you include an external GPS trigger.