MC908AB32CFUE Datasheet, PDF (308/392 Pages) Freescale Semiconductor, Inc – Microcontrollers

Serial Peripheral Interface Module (SPI)
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 16.13.4 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 16.8.2 Mode Fault Error.)
SPR1 and SPR0 — SPI Baud Rate Select Bits
In master mode, these read/write bits select one of four baud rates as
shown in Table 16-4. SPR1 and SPR0 have no effect in slave mode.
Reset clears SPR1 and SPR0.
Table 16-4. SPI Master Baud Rate Selection
SPR1 and SPR0
00
01
10
11
Baud Rate Divisor (BD)
2
8
32
128
Use this formula to calculate the SPI baud rate:
Baud rate = ^{C-----2G-----M}_×----B-O----DU-----T--
where:
CGMOUT = base clock output of the clock generator module (CGM)
BD = baud rate divisor
Technical Data
308
Serial Peripheral Interface Module (SPI)
MC68HC908AB32 — Rev. 1.1
Freescale Semiconductor