What tradeoffs and connection options are there in low cost bidirectional communication between just two microcontrollers?
In this case:
- Master/Slave relationship, bidirectional data flow
- Distance under an inch
- Slave plugs into the master (so ESD protection on the connections is a must).
- The slave micro is pretty dumb, but medium speed data is needed for block I/O from a SD card. Other than the SD card, there is a bit of low speed I/O on the slave unit where speed is not an issue.
- Cheap cheap cheap.
- Pin count is restricted.
- Prefer minimum protocol stack overhead.
Obvious options include SPI, CAN, USB, TTL Level Serial. I2C and 1-Wire are probably too slow. Because of the pin count issue modulating the power supply for data would be ideal, if there were a consumer level chipset that did it, saving two pins over the serial methods.
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