mm912f634 Freescale Semiconductor, Inc, mm912f634 Datasheet - Page 320

• Manufacturer Part Number: mm912f634
• Description: Mm912f634 - Integrated S12 Based Relay Driver With Lin
• Manufacturer: Freescale Semiconductor, Inc

Functional Description and Application Information
4.38.4.2
The SPI operates in slave mode when the MSTR bit in SPI control register 1 is clear.
As long as no more than one slave device drives the system slave’s serial data output line, it is possible for several slaves to
receive the same transmission from a master, although the master would not receive return information from all of the receiving
slaves.
If the CPHA bit in SPI control register 1 is clear, odd numbered edges on the SCK input cause the data at the serial data input
pin to be latched. Even numbered edges cause the value previously latched from the serial data input pin to shift into the LSB or
MSB of the SPI shift register, depending on the LSBFE bit.
If the CPHA bit is set, even numbered edges on the SCK input cause the data at the serial data input pin to be latched. Odd
numbered edges cause the value previously latched from the serial data input pin to shift into the LSB or MSB of the SPI shift
register, depending on the LSBFE bit.
When CPHA is set, the first edge is used to get the first data bit onto the serial data output pin. When CPHA is clear and the SS
input is low (slave selected), the first bit of the SPI data is driven out of the serial data output pin. After the eighth shift, the transfer
is considered complete and the received data is transferred into the SPI data register. To indicate transfer is complete, the SPIF
flag in the SPI status register is set.
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Serial clock
In slave mode, SCK is the SPI clock input from the master.
MISO, MOSI pin
In slave mode, the function of the serial data output pin (MISO) and serial data input pin (MOSI) is determined by the
SPC0 bit and BIDIROE bit in SPI control register 2.
SS pin
The SS pin is the slave select input. Before a data transmission occurs, the SS pin of the slave SPI must be low. SS
must remain low until the transmission is complete. If SS goes high, the SPI is forced into idle state.
The SS input also controls the serial data output pin, if SS is high (not selected), the serial data output pin is high
impedance, and, if SS is low, the first bit in the SPI data register is driven out of the serial data output pin. Also, if the
slave is not selected (SS is high), then the SCK input is ignored and no internal shifting of the SPI shift register occurs.
Although the SPI is capable of duplex operation, some SPI peripherals are capable of only receiving SPI data in a slave
mode. For these simpler devices, there is no serial data out pin.
Slave Mode
When peripherals with duplex capability are used, take care not to simultaneously enable
two receivers whose serial outputs drive the same system slave’s serial data output line.
A change of the CPOL, CPHA, SSOE, LSBFE, MODFEN, SPC0, or BIDIROE bits with
SPC0 set in slave mode will corrupt a transmission in progress and must be avoided.
NOTE
NOTE
Serial Peripheral Interface (S12SPIV4)
MM912F634
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