nRF52832: Why does MOSI stay high after transmitting any byte >7F ?

[awneil]

Using the SDK 15.0.0 SPI example (master) to send a single byte.

Sending 0x00: 

Sending 0x01: 

Sending 0x02: 

Sending 0x04: 

etc ...

Sending 0x7F: 

In all the above, MOSI is low after the byte transmission; BUT ...

Sending 0x80: 

Sending 0xFE: 

So, when the MSB is set, MOSI goes high after the after the byte transmission - even when the last bit transmitted was low!

What's going on here??

[agus.uy]

Seems like it's getting ready to send another byte (same one), loading the MSB.

[Jørgen Holmefjord]

Hi,

Have you tried transmitting data on SPI using registers directly instead of the driver, to see if that makes any difference?

The suggestion from agus.uy sounds reasonable.

Best regards,
Jørgen

[awneil]

No - this is just taking the Nordic example as-is.

In the OP, I'd changed the buffer size to 1 just to make it easier to see.

I get exactly the same effect if I make no code modifications at all, and just edit the last byte of the buffer in the debugger

[landon.ivy]

Hi, did you ever figure out how to fix this?