15.6 SPI Operation Using the Clock Stop Mode
This section explains how to use the McBSP in SPI mode.
15.6.1 SPI Protocol
The SPI protocol is a master-slave configuration with one master device and one or more slave devices. The
interface consists of the following four signals:
• Serial data input (also referred to as slave out/master in, or SOMI)
• Serial data output (also referred to as slave in/master out, or SIMO)
• Shift-clock (also referred to as SPICLK)
• Slave-enable signal (also referred to as SPISTE)
A typical SPI interface with a single slave device is shown in
SPI-compliant
SPICLK
SPISIMO
SPISOMI
SPI-compliant
slave
SPICLK
SPISIMO
SPISOMI
SPISTE
SPISTE
master
Figure 15-36. Typical SPI Interface
The master device controls the flow of communication by providing shift-clock and slave-enable signals. The
slave-enable signal is an optional active-low signal that enables the serial data input and output of the slave
device (device not sending out the clock).
In the absence of a dedicated slave-enable signal, communication between the master and slave is determined
by the presence or absence of an active shift-clock. When the McBSP is operating in SPI master mode and the
SPISTE signal is not used by the slave SPI port, the slave device must remain enabled at all times, and multiple
slaves cannot be used.
15.6.2 Clock Stop Mode
The clock stop mode of the McBSP provides compatibility with the SPI protocol. When the McBSP is configured
in clock stop mode, the transmitter and receiver are internally synchronized so that the McBSP functions as an
SPI master or slave device. The transmit clock signal (CLKX) corresponds to the serial clock signal (SPICLK)
of the SPI protocol, while the transmit frame-synchronization signal (FSX) is used as the slave-enable signal
(SPISTE).
The receive clock signal (MCLKR) and receive frame-synchronization signal (FSR) are not used in the clock stop
mode because these signals are internally connected to their transmit counterparts, CLKX and FSX.
Multichannel Buffered Serial Port (McBSP)
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TMS320x2806x Microcontrollers
SPRUH18I – JANUARY 2011 – REVISED JUNE 2022
Copyright © 2022 Texas Instruments Incorporated
Summary of Contents for TMS320 2806 Series
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