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MC9S08AC60 SPI (Slave) - can SS be permanently tied low (active) with CPHA=1?

Question asked by Michael Fugere on Jul 29, 2016
Latest reply on Aug 2, 2016 by Michael Fugere

I have a design with (2) MC9S08AC60 microcontrollers, (1) SPI Master and (1) SPI slave.   On the slave, I am configuring the SPIC1 bits = SPIE | SPE | CPHA | SSOE and  SPIC2 bits = 0x00 as I need the SPI to run/wake the slave from WAIT instructions.   The SS line on the slave is tied to GND with 10K resistor instead of the Master's SS output pin (which I could change)  I seem to have inconsistent SPI interrupts on the slave, is it necessary for the SS to toggle high-low at all for slave's interrupts to work properly, or can it remain permanently tied low?  I know with CPHA = 0, SS must go high in between successive byte transmissions.  The previous design's chip MC908GP32 had its SS tied low and appeared to work consistently.  The MC9S08AC datasheet indicates the SS must go low at the start of data transmissions, and can remain low for successive bytes, but it doesn't indicate taht the SS could be left active/low all the time.

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