SPI Register Descriptions (SPI_BASE = $1FFFE8)
MOTOROLA
Serial Peripheral Interface (SPI)
11-23
Preliminary
11
11.11.1.2 Data Shift Order (DSO)—Bit 12
This read/write bit determines whether the MSB or LSB bit is transmitted or received first.
Both Master and Slave SPI modules must transmit and receive the same length packets.
Regardless how this bit is set, when reading from the SPDRR or writing to the SPDTR,
the LSB will always be at bit location zero. If the data length is less than 16 bits, the data
will be zero padded on the upper bits.
0 = MSB transmitted first (MSB > LSB)
1 = LSB transmitted first (LSB > MSB)
11.11.1.3 Error Interrupt Enable (ERRIE)—Bit 11
This read/write bit enables the MODF and OVRF bits to generate interrupt requests. Reset
clears the ERRIE bit. The Error Interrupt Enable (ERRIE) bit enables both the MODF and
OVRF bits to generate a receiver/error interrupt request.
0 = MODF and OVRF cannot generate interrupt requests
1 = MODF and OVRF can generate interrupt requests
11.11.1.4 Mode Fault Enable (MODFEN)—Bit 10
This read/write bit, when set to one, allows the MODF flag to be set. If the MODF flag is
set, clearing the MODFEN does not clear the MODF flag.
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. If configured as a Master and
MODFEN = 1, a transmission in progress will stop if SS goes low. It does not affect any
other part of SPI operation.
The Mode Fault Enable (MODFEN) bit can retard the MODF flag from being set. The
retarded bit results in only the OVRF bit being enabled by the ERRIE bit. This enabling
generates receiver/error interrupt requests.
11.11.1.5 SPI Receiver Interrupt Enable (SPRIE)—Bit 9
This read/write bit enables interrupt requests generated by the SPRF bit. The SPRF bit is
set when a full data length transfers from the Shift Register to the Receive Data Register.
The SPI Receiver Interrupt Enable (SPRIE) bit enables the SPRF bit to generate receiver
interrupt requests regardless of the state of the SPE bit. The clearing mechanism for the
SPRF flag is always just a read to the Receive Data Register.
0 = SPRF interrupt requests disabled
1 = SPRF interrupt requests enabled