
ST72321xx-Auto Serial peripheral interface (SPI)
Doc ID 13829 Rev 1 121/243
14 Serial peripheral interface (SPI)
14.1 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
however the SPI interface cannot be a master in a multimaster system.
14.2 Main features
● Full duplex synchronous transfers (on 3 lines)
● Simplex synchronous transfers (on 2 lines)
● Master or slave operation
● 6 master mode frequencies (f
CPU
/4 max.)
● f
CPU
/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.
14.3 General description
Figure 55 shows the serial peripheral interface (SPI) block diagram. There are three
registers:
● 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 input by SPI slaves)
● SS (Slave select): This input signal acts as a ‘chip select’ to let the SPI master
communicate with slaves individually and to avoid contention on the data lines. Slave
SS
inputs can be driven by standard I/O ports on the master MCU.
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