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12.3 SPI Operation
This section describes the various modes of operation of the SPI. Included are explanations of the operational
modes, interrupts, data format, clock sources, and initialization. Typical timing diagrams for data transfers are
given.
12.3.1 Introduction to Operation
shows typical connections of the SPI for communications between two controllers: a master and a
slave.
The master transfers data by sending the SPICLK signal. For both the slave and the master, data is shifted out
of the shift registers on one edge of the SPICLK and latched into the shift register on the opposite SPICLK clock
edge. If the CLK_PHASE bit is high, data is transmitted and received a half-cycle before the SPICLK transition.
As a result, both controllers send and receive data simultaneously. The application software determines whether
the data is meaningful or dummy data. There are three possible methods for data transmission:
• Master sends data; slave sends dummy data.
• Master sends data; slave sends data.
• Master sends dummy data; slave sends data.
The master can initiate data transfer at any time because it controls the SPICLK signal. The software, however,
determines how the master detects when the slave is ready to broadcast data.
The SPI can operate in master or slave mode. The MASTER_SLAVE bit selects the operating mode and the
source of the SPICLK signal.
SPI master (master/slave = 1)
SPI slave (master/slave = 0)
SPIRXBUF.15−0
Serial input buffer
SPIRXBUF
Shift register
(SPIDAT)
SPITXBUF.15−0
Serial transmit buffer
SPITXBUF
Processor 1
SPIDAT.15−0
SPICLK
SPISOMI
SPISTE
SPISIMO
SPICLK
SPISOMI
SPISTE
SPISIMO
Slave in/
master out
SPI
strobe
Slave out/
master in
Serial
clock
SPIRXBUF.15−0
Serial input buffer
SPIRXBUF
Shift register
(SPIDAT)
SPITXBUF.15−0
Serial transmit buffer
SPITXBUF
SPIDAT.15−0
Processor 2
LSB
MSB
LSB
MSB
Figure 12-4. SPI Master/Slave Connection
is a block diagram of the SPI module showing all of the basic control blocks available on the SPI
module.
Serial Peripheral Interface (SPI)
766
TMS320x2806x Microcontrollers
SPRUH18I – JANUARY 2011 – REVISED JUNE 2022
Copyright © 2022 Texas Instruments Incorporated
Summary of Contents for TMS320 2806 Series
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