[RIIM] Do I need an external pull-up resistor on the SPI CS (chip Select)?

Yes. During bootloading, the device uses SPI but with the internal Cs (chip Select). So any other external device with the CS low might cause bus contention as now two devices are fighting for control of the same line.

Last Update: September 29, 2021  

September 29, 2021   311    RIIM Q&A