(This is more of an electronics question)
I have 7 SPI devices connected along a 20 pin ribbon cable. The cable is between 7 to 8 feet, long. The distance between the µC and the last device is the full length (approx 8 feet away). When I send zeros (0x0), I am able to get the data back correctly. However, when I try to send any commands (e.g. 0x36), which is supposed to have a response (0x2E88) I am getting wild, unpredictable values instead. I need some idea as to what could be wrong. I know this description is far to vague to properly diagnose the problem, but I’ve got to try something; can’t just stay stuck for another month.
General Facts about the system:
Daisy Chain stepper motor drivers (dSpin l6470’s) supporting up to 9 drivers.
Distance between µC and last driver in the chain is currently 8 feet.
Logic VCC is 3.3 volts (3.29 measured)
I am able to drive the closest motor, if I bypass all the others.
There appear to be no shorts or open circuits
Driver VDD is 12 Volts (12.1 measured)
EM from one signal line to another is possible (which would be really bad)