Spi 3-Wire Mode Description; Spi 3-Wire Master Mode; 4-Wire Vs. 3-Wire Spi Pin Functions - Texas Instruments Concerto F28M35 Series Technical Reference Manual

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Enhanced SPI Module Overview

SPI FIFO mode

12.1.7 SPI 3-Wire Mode Description

SPI 3-wire mode allows for SPI communication over 3 pins instead of the normal 4 pins.

In master mode, if the TRIWIRE (SPIPRI.0) bit is set, enabling 3-wire SPI mode, SPISIMOx becomes the

bi-directional SPIMOMIx (SPI master out, master in) pin, and SPISOMIx is no longer used by the SPI. In

slave mode, if the TRIWIRE bit is set, SPISOMIx becomes the bi-directional SPISISOx (SPI slave in, slave

out) pin, and SPISIMOx is no longer used by the SPI.

The table below indicates the pin function differences between 3-wire and 4-wire SPI mode for a master

and slave SPI.

Because in 3-wire mode, the receive and transmit paths within the SPI are connected, any data

transmitted by the SPI module is also received by itself. The application software must take care to

perform a dummy read to clear the SPI data register of the additional received data.

The TALK bit (SPICTL.1) plays an important role in 3-wire SPI mode. The bit must be set to transmit data

and cleared prior to reading data. In master mode, in order to initiate a read, the application software must

write dummy data to the SPI data register (SPIDAT or SPIRXBUF) while the TALK bit is cleared (no data

is transmitted out the SPIMOMI pin) before reading from the data register.

C28 Serial Peripheral Interface (SPI)

Table 12-4. SPI Interrupt Flag Modes (continued)

SPI Interrupt

FIFO receive

Transmit empty

Table 12-5. 4-wire vs. 3-wire SPI Pin Functions

3-wire SPI (Master)

Figure 12-8. SPI 3-wire Master Mode

3-wire SPI(Slave)

SPRUH22I – April 2012 – Revised November 2019

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