spim_csx
mcspi-031
spim_somi
spim_clk
Transmitter buffer
Shift register
Master
Control
Receiver register
Master SPI shift register
Initial
After 8
clock cycles
WordA
WordB
(single line)
Slave SPI shift register
Initial
After 8
clock cycles
WordB
WordC
Control
Slave
(transmit only)
Transmitter buffer
Shift register
Public Version
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McSPI Functional Description
Figure 20-19. SPI Half-Duplex Transmission (Transmit-Only Slave)
20.5.3.4 Slave Receive-Only Mode
The slave receive mode is programmable (set the SPIm.
[13:12] TRM field (with x=0) to
0x1).
In receive-only mode, the
register must be loaded before the McSPI is selected by an
external SPI master device. The
register content is always loaded into the shift register
whether it is updated or not. The TXx_UNDERFLOW event is activated accordingly and does not prevent
transmission.
When an SPI word transfer completes (the SPIm.
0[2] EOT bit (with x=0) is set to 1), the
received data is transferred to the channel receive register.
To use the McSPI as a slave receive-only device, the TXx_EMPTY and TXx_UNDERFLOW interrupts and
the DMA write requests must be disabled due to the
register state.
For a full-duplex transmission, the serial clock (spim_clk) synchronizes shifting and sampling of the
information on the single serial data line. For full duplex, two data lines are required. If spim_clk
synchronizes on a single serial data line, the data line should be half-duplex.
shows an example of a half-duplex system with a master device on the left and a
receive-only slave device on the right. Each time a bit transfers out from the master, 1 bit transfers in from
the slave. After eight cycles of the serial clock spim_clk, Word A transfers from the master to the slave.
3001
SWPU177N – December 2009 – Revised November 2010
Multichannel SPI
Copyright © 2009–2010, Texas Instruments Incorporated