MC68HC908GR16 Datasheet, PDF (237/310 Pages) Motorola, Inc – Microcontrollers

Freescale Semiconductor, Inc.
Serial Peripheral Interface (SPI) Module
I/O Registers
NOTE:
OVRF — Overflow Bit
This clearable, read-only flag is set if software does not read the byte in the
receive data register before the next full byte enters the shift register. In an
overflow condition, the byte already in the receive data register is unaffected,
and the byte that shifted in last is lost. Clear the OVRF bit by reading the SPI
status and control register with OVRF set and then reading the receive data
register. Reset clears the OVRF bit.
1 = Overflow
0 = No overflow
MODF — Mode Fault Bit
This clearable, read-only flag is set in a slave SPI if the SS pin goes high during
a transmission with the MODFEN bit set. In a master SPI, the MODF flag is set
if the SS pin goes low at any time with the MODFEN bit set. Clear the MODF bit
by reading the SPI status and control register (SPSCR) with MODF set and then
writing to the SPI control register (SPCR). Reset clears the MODF bit.
1 = SS pin at inappropriate logic level
0 = SS pin at appropriate logic level
SPTE — SPI Transmitter Empty Bit
This clearable, read-only flag is set each time the transmit data register
transfers a byte into the shift register. SPTE generates an SPTE CPU interrupt
request or an SPTE DMA service request if the SPTIE bit in the SPI control
register is set also.
Do not write to the SPI data register unless the SPTE bit is high.
During an SPTE CPU interrupt, the CPU clears the SPTE bit by writing to the
transmit data register.
Reset sets the SPTE bit.
1 = Transmit data register empty
0 = Transmit data register not empty
MODFEN — Mode Fault Enable Bit
This read/write bit, when set to 1, allows the MODF flag to be set. If the MODF
flag is set, clearing the MODFEN does not clear the MODF flag. If the SPI is
enabled as a master and the MODFEN bit is low, then the SS pin is available as
a general-purpose I/O.
If the MODFEN bit is set, then this pin is not available as a general-purpose I/O.
When the SPI is enabled as a slave, the SS pin is not available as a
general-purpose I/O regardless of the value of MODFEN. See 16.12.4 SS
(Slave Select).
If the MODFEN bit is low, the level of the SS pin does not affect the operation
of an enabled SPI configured as a master. For an enabled SPI configured as a
slave, having MODFEN low only prevents the MODF flag from being set. It does
not affect any other part of SPI operation. See 16.7.2 Mode Fault Error.
MC68HC908GR16 — Rev. 1.0
MOTOROLA
Serial Peripheral Interface (SPI) Module
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Data Sheet
237