FRDM-KL25Z MOSI and MISO idle states in SPI

[aaronm]

What are the default idle states - low or high - for the MOSI and MISO lines on a KL25Z?  From my testing, it looks like they both idle HIGH.  But a breakout board I'm using for SD cards seems to work better with MOSI idle LOW, and MISO idle HIGH.  I've tried setting the port configuration for the MOSI line LOW, but it doesn't actually go low.  I've also tried using a MOSFET 2n7000 transistor as an inverter to have idle HIGH signal inverted to idle LOW, but that causes problems with the MISO line.

I've looked through the KL25 Sub Family Reference Manual, but I did not see this information anywhere.

[aaronm · Accepted solution]

I've determined that both MOSI and MISO idle at HIGH on the KL25Z in SPI mode.  Here's a screen capture of my scope with a working command and response for an SD card in SPI mode.  Yellow is MOSI; purple is MISO.  You can't see the command and response details, since I captured the entire 6 commands, but you can see the dips to 0.

[aaronm]

Here's a closer look at the signals.  This is the cmd55/acmd41, and cmd58 sequence, with responses.