Why a dummy read SPI is required for BMP280?

[elrhoul]

Can you please explain why we need a dummy SPI after switching to SPI protocol? and What is the minimum delay time needed after dummy SPI read?

[elrhoul · Accepted solution]

BMP280 supports both I2C and SPI interface but has no PS (protocol select) pin.

It starts with the I2C interface enabled. If there is a raising edge on the CSB line, it will switch to the SPI protocol. There should be at least a 140us delay after the first SPI dummy read operation to make sure the bus switch was successful.