HCS08 datasheet(222/316 Pages) NXP

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Serial Peripheral Interface (S08SPIV3)

MC9S08SG8 MCU Series Data Sheet, Rev.8

222

Freescale Semiconductor

The most common uses of the SPI system include connecting simple shift registers for adding input or

output ports or connecting small peripheral devices such as serial A/D or D/A converters. Although

Figure 15-2 shows a system where data is exchanged between two MCUs, many practical systems involve

simpler connections where data is unidirectionally transferred from the master MCU to a slave or from a

slave to the master MCU.

15.1.2.2

SPI Module Block Diagram

Figure 15-3 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 SPID) and gets transferred to the SPI shift

double-buffered receiver where it can be read (read from SPID). 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.

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