CLKOUT
SPICLK
2 cycles
3 cycles
2 cycles
SPICLK cycle
number
1
2
3
4
5
6
7
8
SPICLK
(Falling edge
without delay)
SPICLK
(Falling edge
with delay)
SPISIMO/
SPISOMI
SPISTE
MSB
LSB
Note:
Previous data bit
(Into slave)
Receive latch
points
SPICLK
(Rising edge
without delay)
SPICLK
(Rising edge
with delay
)
See note
Enhanced SPI Module Overview
954
SPRUH22I – April 2012 – Revised November 2019
Copyright © 2012–2019, Texas Instruments Incorporated
C28 Serial Peripheral Interface (SPI)
The selection procedure for the SPI clocking scheme is shown in
. Examples of these four
clocking schemes relative to transmitted and received data are shown in
.
(1)
The description of CLOCK PHASE and CLOCK POLARITY differs between manufacturers. For proper operation, select the
desired waveform to determine the PHASE and POLARITY settings.
Table 12-3. SPI Clocking Scheme Selection Guide
SPICLK Scheme
CLOCK POLARITY
(SPICCR.6)
CLOCK PHASE
(SPICTL.3)
(1)
Rising edge without delay
0
0
Rising edge with delay
0
1
Falling edge without delay
1
0
Falling edge with delay
1
1
Figure 12-4. SPICLK Signal Options
For the SPI, SPICLK symmetry is retained only when the result of (1) is an even value. When
( 1) is an odd value and SPIBRR is greater than 3, SPICLK becomes asymmetrical. The low
pulse of SPICLK is one CLKOUT longer than the high pulse when the CLOCK POLARITY bit is clear (0).
When the CLOCK POLARITY bit is set to 1, the high pulse of the SPICLK is one CLKOUT longer than the
low pulse, as shown in
Figure 12-5. SPI: SPICLK-CLKOUT Characteristic When (BRR + 1) is Odd, BRR > 3, and CLOCK
POLARITY = 1