mc68hc708mp16 Freescale Semiconductor, Inc, mc68hc708mp16 Datasheet - Page 256

• Manufacturer Part Number: mc68hc708mp16
• Description: M68hc08 Microcontrollers
• Manufacturer: Freescale Semiconductor, Inc

Serial Peripheral Interface Module (SPI)
Technical Data
256
Only a master SPI module can initiate transmissions. Software begins
the transmission from a master SPI module by writing to the transmit
data register. If the shift register is empty, the byte immediately transfers
to the shift register, setting the SPI transmitter empty bit, SPTE. The byte
begins shifting out on the MOSI pin under the control of the serial clock.
See
The SPR1 and SPR0 bits control the baud rate generator and determine
the speed of the shift register. (See
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
register. In normal operation, SPRF signals the end of a transmission.
Software clears SPRF by reading the SPI status and control register with
SPRF set and then reading the SPI data register. Writing to the SPI data
register clears the SPTE bit.
When the DMAS bit is set, the SPI status and control register does not
have to be read to clear the SPRF bit. A read of the SPI data register by
the CPU clears the SPRF bit. A write to the SPI data register by the CPU
clears the SPTE bit.
Figure
SHIFT REGISTER
GENERATOR
MASTER MCU
BAUD RATE
Serial Peripheral Interface Module (SPI)
Figure 13-3. Full-Duplex Master-Slave Connections
13-3.
MISO
MOSI
SPSCK
SS
V
13.14.2 SPI Status and Control
DD
SPSCK
MISO
MOSI
MC68HC708MP16
SS
Freescale Semiconductor
SHIFT REGISTER
SLAVE MCU
—
Rev. 3.1