HCS08 datasheet(245/374 Pages) NXP

245 / 374 page

Serial Peripheral Interface (S08SPI16V1)

MC9S08JM60 Series Data Sheet, Rev. 5

Freescale Semiconductor

245

15.1.4.1

SPI System Block Diagram

Figure 15-3 shows the SPI modules of two MCUs connected in a master-slave arrangement. The master

device initiates all SPI data transfers. During a transfer, the master shifts data out (on the MOSI pin) to the

slave while simultaneously shifting data in (on the MISO pin) from the slave. The transfer effectively

exchanges the data that was in the SPI shift registers of the two SPI systems. The SPSCK signal is a clock

output from the master and an input to the slave. The slave device must be selected by a low level on the

slave select input (SS pin). In this system, the master device has configured its SS pin as an optional slave

select output.

Figure 15-3. SPI System Connections

15.1.4.2

SPI Module Block Diagram

Figure 15-4 is a block diagram of the SPI module. The central element of the SPI is the SPI shift register.

Data is written to the double-buffered transmitter (write to SPIxDH:SPIxDL) and gets transferred to the

SPI shift register at the start of a data transfer. After shifting in 8 or 16 bits (as determined by SPIMODE

bit) of data, the data is transferred into the double-buffered receiver where it can be read (read from

SPIxDH:SPIxDL). Pin multiplexing logic controls connections between MCU pins and the SPI module.

When the SPI is configured as a master, the clock output is routed to the SPSCK pin, the shifter output is

routed to MOSI, and the shifter input is routed from the MISO pin.

When the SPI is configured as a slave, the SPSCK pin is routed to the clock input of the SPI, the shifter

output is routed to MISO, and the shifter input is routed from the MOSI pin.

In the external SPI system, simply connect all SPSCK pins to each other, all MISO pins together, and all

MOSI pins together. Peripheral devices often use slightly different names for these pins.

SPI SHIFTER

CLOCK

GENERATOR

SPI SHIFTER

SPSCK

MISO

MOSI

SPSCK

MISO

MOSI

MASTER

SLAVE

8 OR 16 BITS

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