mcf51ac256a Freescale Semiconductor, Inc, mcf51ac256a Datasheet - Page 440

• Manufacturer Part Number: mcf51ac256a
• Description: Mcf51ac Flexis
• Manufacturer: Freescale Semiconductor, Inc

8-Bit Serial Peripheral Interface (SPIV3)
The service routine should also clear the flag bit(s) before returning from the ISR (usually near the
beginning of the ISR).
19.5.3
Mode Fault Detection
A mode fault occurs and the mode fault flag (MODF) sets when a master SPI device detects an error on
the SS pin (provided the SS pin is configured as the mode fault input signal). The SS pin is configured as
the mode fault input signal when MSTR and MODFEN is set, and SSOE is clear.
The mode fault detection feature is used in a system where more than one SPI device might become a
master at the same time. The error is detected when a master’s SS pin is low, indicating that some other
SPI device is trying to address this master as if it were a slave. This could indicate a harmful output driver
conflict, so the mode fault logic is designed to disable all SPI output drivers when such an error is detected.
When a mode fault is detected, MODF is set and MSTR is cleared to change the SPI configuration back
to slave mode. The output drivers on the SPSCK, MOSI, and MISO (if not bidirectional mode) are
disabled.
MODF is cleared by reading it while it is set, then writing to the SPI1C1 register. Software should verify
the error condition has been corrected before changing the SPI back to master mode.
MCF51AC256 ColdFire Integrated Microcontroller Reference Manual, Rev. 5
19-14
Freescale Semiconductor