MC68HC05C8A Datasheet, PDF (95/158 Pages) Motorola, Inc – Microcontrollers

Serial Peripheral Interface (SPI)
SPI Registers
WCOL — Write Collision Bit
The write collision bit is set when an attempt is made to write to the
serial peripheral data register while data transfer is taking place. If
CPHA is 0, a transfer is said to begin when SS goes low and the
transfer ends when SS goes high after eight clock cycles on SCK.
When CPHA is 1, a transfer is said to begin the first time SCK
becomes active while SS is low. The transfer ends when the SPIF flag
gets set. Clearing the WCOL bit is accomplished by reading the SPSR
(with WCOL set) followed by an access to SPDR.
Bit 5 — Not implemented
This bit always reads as 0.
MODF — Mode Fault Flag
The mode fault flag indicates that there may have been a multi-master
conflict for system control and allows a proper exit from system
operation to a reset or default system state. The MODF bit is normally
clear and is set only when the master device has its SS pin pulled low.
Setting the MODF bit affects the internal serial peripheral interface
system in these ways:
•An SPI interrupt is generated if SPIE = 1.
•The SPE bit is cleared. This disables the SPI.
•The MSTR bit is cleared, thus forcing the device into the slave
mode.
Clearing the MODF bit is accomplished by reading the SPSR (with
MODF set), followed by a write to the SPCR. Control bits SPE and
MSTR may be restored by user software to their original state after
the MODF bit has been cleared.
Bits 3–0 — Not Implemented
These bits always reads as 0.
MC68HC05C8A • MC68HCL05C8A • MC68HSC05C8A — Rev. 5.0
MOTOROLA
Serial Peripheral Interface (SPI)
Technical Data
95