We know there are 4 modes in standard 4 wire SPI communication.

Which are a result of 2 options for Clock phase (CPHA) and Clock polarity (CPOL). I understand how these 4 different modes work.

I am aware of the fact the motorola did not fix the standard for CPOL and CPHA and hence manufactures were free to chose their configuration and in order for a manufacture to work with all others they also had to keep this flexibility in the hardware.

However if i could chose on both master and slave, is there any case when i would select mode 1,2 or 3 instead of the default mode 0.


1 Answer 1


You would select what is most convenient for you.

Remember that as the modes are not standardized by numbers, you would choose what you want based on what you want to see on the bus, and then select the mode based on whichever mode number or CPOL/CPHA settings happen to select that bus protocol.

Two of the modes require a clock edge before slave can output the first data bit on the bus.

Two other modes allow the slave to output the first data bit on the bus before the first clock edge.

That can be an used for something if you find use for such a feature, such as a handshake when data is available for actually start clocking data out.

Otherwise it makes no difference for the data transfer itself.

It may make a difference when two subsystems are separately powered so either one can be powered off, or how to set sefault pull-up or pull-down reaistances if the two subsystems are detachable with some cable or connector.


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