Datasheet

• Master out/slave in (MOSI)

• Master in/slave out (MISO)

An SPI transfer is initiated in the master SPI device by reading the SPI status register

(SPIx_S) when SPTEF = 1 and then writing data to the transmit data buffer (write to

SPIxD ). When a transfer is complete, received data is moved into the receive data buffer.

The SPIxD register acts as the SPI receive data buffer for reads and as the SPI transmit

data buffer for writes.

The clock phase control bit (CPHA) and a clock polarity control bit (CPOL) in the SPI

Control Register 1 (SPIx_C1) select one of four possible clock formats to be used by the

SPI system . The CPOL bit simply selects a non-inverted or inverted clock . The CPHA

bit is used to accommodate two fundamentally different protocols by sampling data on

odd numbered SPSCK edges or on even numbered SPSCK edges .

The SPI can be configured to operate as a master or as a slave. When the MSTR bit in

SPI control register 1 is set, master mode is selected, when the MSTR bit is clear, slave

mode is selected.

16.4.2 Master Mode

The SPI operates in master mode when the MSTR bit is set. Only a master SPI module

can initiate transmissions. A transmission begins by reading the SPIx_S register while

SPTEF = 1 and writing to the master SPI data registers. If the shift register is empty, the

byte immediately transfers to the shift register. The data begins shifting out on the MOSI

pin under the control of the serial clock.

• SPSCK

• The SPR3, SPR2, SPR1, and SPR0 baud rate selection bits in conjunction with

the SPPR2, SPPR1, and SPPR0 baud rate preselection bits in the SPI Baud Rate

transmission. The SPSCK pin is the SPI clock output. Through the SPSCK pin,

the baud rate generator of the master controls the shift register of the slave

peripheral.

• MOSI, MISO pin

• In master mode, the function of the serial data output pin (MOSI) and the serial

data input pin (MISO) is determined by the SPC0 and BIDIROE control bits.

•

SS pin

Chapter 16 8-Bit Serial Peripheral Interface (8-bit SPI)

MC9S08PA60 Reference Manual, Rev. 1, 9/2012

Freescale Semiconductor, Inc. 437