MC68HC708MP16 Datasheet, PDF (281/398 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 13.13.4 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 13.8.2 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 13-4. SPR1 and SPR0 have no effect in slave mode.
Reset clears SPR1 and SPR0.
Table 13-4. SPI Master Baud Rate Selection
SPR1:SPR0
00
01
10
11
Baud Rate Divisor (BD)
2
8
32
128
Use the following formula to calculate the SPI baud rate:
where:
Baud rate = ^{C-----2G-----M}_×----B-O----DU-----T--
CGMOUT = base clock output of the clock generator module (CGM)
BD = baud rate divisor
MC68HC708MP16 — Rev. 3.1
Freescale Semiconductor
Serial Peripheral Interface Module (SPI)
Technical Data
281