I'm attempting to read some accelerometer values out of the 300ZA using SPI. The 300ZA was connected to a Teensy 3.6 (wiring checked and checked again) but no registers could be read successfully. After further checking, an osciliscope was deployed, and strange behaviour on the CLK line was discovered. Further digging showed that this line seemed to be being driven by both the 300ZA and the Teensy.
In the following screengrabs, Yellow = clock, Blue = chip slect, Green = MOSI, Red = MISO. Please disregard the fact that MOSI (Green) is far too small, this is a fault on the probe.
As we can see, the Teensy puts chip select low then a read command is sent over MOSI. The 300ZA makes no attempt to respond, presumably because the clock is not behaving properly?
With the 300ZA disconected from the Teensy, we see that the clock oscillates between 0 and 3.3V as you'd expect.
With the 300ZA connected to the Teensy, the clock oscillates between 1 and 3.3V.
If we disconnect the teensy clock out from the 300ZA clock in (leaving all other pins connected), then measure the 300ZA's clock in pin, we see the clock line is held high and occasionally oscillated.
Is it normal for the SPI clock pin (pin 3) on the 300ZA? It seems like odd behavior to me since this pin is supposed to be an input? I am assuming it's an input from the 300ZI datasheet, as I was told in this thread that the 300ZA is identical to the 300ZA. This issue has caused me to dig even deeper for a 300ZA datasheet, and I was eventually able to find an archived one here. It seems to imply that the SPI clock pin (pin 3) on the 300ZA is in fact an output?!
Any help on this issue would be much appreciated.