Serial Peripheral Interface Module (SPI)
Functional Description
MC68HC908MR16/MC68HC908MR32 — Rev. 4.0 Advance Information
MOTOROLA Serial Peripheral Interface Module (SPI) 251
Figure 13-3. Full-Duplex Master-Slave Connections
The SPR1 and SPR0 bits control the baud rate generator and determine
the speed of the shift register. See 13.13.2 SPI Status and Control
Register. Through the SPSCK pin, the baud-rate generator of the
master also controls the shift register of the slave peripheral.
As the byte shifts out on the MOSI pin of the master, another byte shifts
in from the slave on the master’s MISO pin. The transmission ends when
the receiver full bit, SPRF, becomes set. At the same time that SPRF
becomes set, the byte from the slave transfers to the receive data
Addr. Register Name Bit 7 6 5 4 3 2 1 Bit 0
$0044 SPI Control Register
(SPCR)
See page 270.
Read: SPRIE R SPMSTR CPOL CPHA SPWOM SPE SPTIE
Write:
Reset:00101000
$0045 SPI Status and Control
Register (SPSCR)
See page 272.
Read: SPRF ERRIE OVRF MODF SPTE MODFEN SPR1 SP R0
Write:R RRR
Reset:00001000
$0046 SPI Data Register
(SPDR)
See page 275.
Read: R7 R6 R5 R4 R3 R2 R1 R0
Write: T7 T6 T5 T4 T3 T2 T1 T0
Reset: Unaffected by reset
R= Reserved
Figure 13-2. SPI I/O Register Summary
SHIFT REGISTER
SHIFT REGISTER
BAUD RATE
GENERATOR
MASTER MCU SLAVE MCU
VDD
MOSI MOSI
MISO MISO
SPSCK SPSCK
SS SS