We have an application in which we have two PCBs, each carrying an AtMega 162, within a commercial machine.
As a system enhancement, we have decided that it would be a good thing if we could make one of the boards pass a single byte of data to the other, each millisecond, to achieve a level of operational synchronisation between the two.
The MISO/MOSI/SCK interface looks ideal for the job!
However, as that is also the reprogramming interface, I gather that we can't put buffers or transistors in the way and we are going to have to connect the three signals directly together.
Anybody got any experience of this? How far ought we be able to space the boards apart and still expect reliable comms. At what kind of transmission rate? I know that we could implement some flavour of protocol and checksumming, but just passing a byte (reliably) per millisecond would make our lives very easy.
The host machine should not be very noisy electrically, though there will be low power stepper motors running and the occasional solenoid firing.
Any "wet finger in the air" advice from you hardware bods out there?