Post History

Unterminated SPI bus needs expansion board to work properly

I'm supporting a piece of legacy hardware that routes the SPI bus through a set of headers to an expansion board.  Since the expansion board doesn't actually use the SPI bus, we simply ignored the incoming SPI lines when we revised the expansion board.

However, we are now experiencing seemingly random errors on the SPI bus, as it communicates with two devices on the main board.  Since there is no source or end termination present on the SPI bus, it makes me wonder if the extra capacitance of the expansion board was enough to prevent reflections.

The main board will not be revised for some time, so I would like to figure out what modification (extra capacitance? resistance?) I could make to the expansion boards that would help prevent SPI reflections, or if there are other possibilities that I'm not thinking of.

I should also mention that this is a low-power, battery-operated system.  The top speed for SPI communication on this board is about 1MHz.

It seems like a similar question to this:
https://electronics.stackexchange.com/questions/33372/spi-bus-termination-considerations