ST72344 datasheet(87/191 Pages) STMICROELECTRONICS

87 / 191 page

ST72340, ST72344, ST72345

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ON-CHIP PERIPHERALS (cont’d)

11.4 SERIAL PERIPHERAL INTERFACE (SPI)

11.4.1 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.

11.4.2 Main Features

■ Full duplex synchronous transfers (on three

lines)

■ Simplex synchronous transfers (on two lines)

■ Master or slave operation

■ 6 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.

11.4.3 General Description

Figure 1 on page 3 shows the serial peripheral in-

terface (SPI) block diagram. There are three regis-

ters:

– SPI Control Register (SPICR)

– SPI Control/Status Register (SPICSR)

– SPI Data Register (SPIDR)

The SPI is connected to external devices through

four 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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