ST72561 datasheet(112/262 Pages) STMICROELECTRONICS

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ST72561

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10.6 SERIAL PERIPHERAL INTERFACE (SPI)

10.6.1 Introduction

The Serial Peripheral Interface (SPI) allows full-

duplex, synchronous, serial communication with

external devices. An SPI system may consist of a

master and one or more slaves or a system in

which devices may be either masters or slaves.

10.6.2 Main Features

Full duplex synchronous transfers (on 3 lines)

Simplex synchronous transfers (on 2 lines)

Master or slave operation

Six master mode frequencies (fCPU/4 max.)

fCPU/2 max. slave mode frequency (see note)

SS Management by software or hardware

Programmable clock polarity and phase

End of transfer interrupt flag

Write collision, Master Mode Fault and Overrun

flags

Note: In slave mode, continuous transmission is

not possible at maximum frequency due to the

software overhead for clearing status flags and to

initiate the next transmission sequence.

10.6.3 General Description

Figure 70 shows the serial peripheral interface

(SPI) block diagram. There are 3 registers:

– SPI Control Register (SPICR)

– SPI Control/Status Register (SPICSR)

– SPI Data Register (SPIDR)

The SPI is connected to external devices through

4 pins:

– MISO: Master In / Slave Out data

– MOSI: Master Out / Slave In data

– SCK: Serial Clock out by SPI masters and in-

put by SPI slaves

– SS: Slave select:

This input signal acts as a ‘chip select’ to let

the SPI master communicate with slaves indi-

vidually and to avoid contention on the data

lines. Slave SS inputs can be driven by stand-

ard I/O ports on the master Device.

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