32MHz SPI Reducing Drive Strength

[mredp]

Hi,

I am using the SPI at 32MHz. I would like to add 0R series resistors to the SPI lines so that I have the option to add a 10R or so to mitigate any emissions or immunity problems during CE testing. However, I do not have much spare space with our PCB size constraints. 

I believe that reducing the drive strength may provide me with the same capability as the additional resistors. However, I am unsure if this will affect functionality of the SPI.

I know you recommend using high drive when using SPI at 32Mhz. Is this just a recommendation or is this essential? Should I avoid this as a solution?

Thanks for your help! 

[Turbo J]

mredp said:

is this essential?

It is.

Without high drive, the SPI clock signal turns into a sinus curve somewhere around 2 MHz. Just hook up a scope and measure using different drive strenghts.

Note that you could save some board space by using a resistor network instead of individual resistors.