Freescale Semiconductor MC68HC908MR32 - Manual (Page 211)

I/O Registers
MC68HC908MR32 • MC68HC908MR16 Data Sheet, Rev. 6.1
Freescale Semiconductor 211
SPRIE — SPI Receiver Interrupt Enable Bit
This read/write bit enables CPU interrupt requests generated by the SPRF bit. The SPRF bit is set
when a byte transfers from the shift register to the receive data register. Reset clears the SPRIE bit.
1 = SPRF CPU interrupt requests enabled
0 = SPRF CPU interrupt requests disabled
SPMSTR — SPI Master Bit
This read/write bit selects master mode operation or slave mode operation. Reset sets the SPMSTR
bit.
1 = Master mode
0 = Slave mode
CPOL — Clock Polarity Bit
This read/write bit determines the logic state of the SPSCK pin between transmissions. See Figure
15-5 and Figure 15-7 . To transmit data between SPI modules, the SPI modules must have identical
CPOL values. Reset clears the CPOL bit.
CPHA — Clock Phase Bit
This read/write bit controls the timing relationship between the serial clock and SPI data. See Figure
15-5 and Figure 15-7 . To transmit data between SPI modules, the SPI modules must have identical
CPHA bits. When CPHA = 0, the SS pin of the slave SPI module must be set to logic 1 between bytes.
See
Figure 15-13 . Reset sets the CPHA bit.
When CPHA = 0 for a slave, the falling edge of SS indicates the beginning of the transmission. This
causes the SPI to leave its idle state and begin driving the MISO pin with the MSB of its data, once the
transmission begins, no new data is allowed into the shift register from the data register. Therefore,
the slave data register must be loaded with the desired transmit data before the falling edge of SS. Any
data written after the falling edge is stored in the data register and transferred to the shift register at
the current transmission.
When CPHA = 1 for a slave, the first edge of the SPSCK indicates the beginning of the transmission.
The same applies when SS is high for a slave. The MISO pin is held in a high-impedance state, and
the incoming SPSCK is ignored. In certain cases, it may also cause the MODF flag to be set. See
15.6.2 Mode Fault Error . A logic 1 on the SS pin does not in any way affect the state of the SPI state
machine.
SPWOM — SPI Wired-OR Mode Bit
This read/write bit disables the pullup devices on pins SPSCK, MOSI, and MISO so that those pins
become open-drain outputs.
1 = Wired-OR SPSCK, MOSI, and MISO pins
0 = Normal push-pull SPSCK, MOSI, and MISO pins
Address: $0044
Bit 7 6 5 4 3 2 1 Bit 0
Read:
SPRIE R SPMSTR CPOL CPHA SPWOM SPE SPTIE
Write:
Reset: 0 0 1 0 1 0 0 0
R = Reserved
Figure 15-14. SPI Control Register (SPCR)