MPC823 datasheet(54/74 Pages) MOTOROLA

54 / 74 page

Communication Processor Module

16-432

MPC823 REFERENCE MANUAL

MOTOROLA

16.12.2 SPI Clocking and Pin Functions

You can configure the serial peripheral interface as a master for the serial channel or as a

slave. You can also use it in a multimaster environment. When the serial peripheral interface

is a master, use the SPI baud rate generator to generate the SPI transmit and receive

clocks. It takes its input from the BRGCLK, which is generated in the clock synthesizer of

the MPC823, specifically for the SPI baud rate generator and the other three baud rate

generators in the communication processor module.

The SPIMISO pin is an input in master mode and an output in slave mode. It follows then,

that the SPIMOSI pin is an output in master mode and an input in slave mode. The SPIMOSI

and SPIMISO pins change functionality between master and slave mode to support a

multimaster configuration that allows communication from one serial peripheral interface to

another with the same hardware configuration.

When the serial peripheral interface is in master mode, SPICLK is the clock output signal

that shifts in the received data from the SPIMISO pin and shifts out the transmitted data to

the SPIMOSI pin. Additionally, an SPI master device must provide a slave-select signal

output to enable the SPI slave devices. You can implement this by using one of the MPC823

general-purpose I/O pins. The SPISEL pin must not be asserted while the serial peripheral

interface is in master mode or an error will occur.

When the serial peripheral interface is in slave mode, SPICLK is the clock input signal that

shifts in the received data from the SPIMOSI pin and shifts out the transmitted data to the

SPIMISO pin. The SPISEL pin provided by the MPC823 is the enable input to the SPI slave.

When the serial peripheral interface is operating in a multimaster environment, the SPISEL

pin is still an input and is used to detect an error condition when more than one master is

operating.

Using the fields in the SPI mode register, you can select any of the four combinations of the

gated SPICLK phase and polarity. The SPI pins can also be configured as open-drain pins

to support a multimaster configuration in which the same SPI pin is driven by the MPC823

or an external SPI device.

MPC823 Arkusz danych(PDF) 54 Page - Motorola, Inc