CKPH CKPL
Cycle#
UCxCLK
UCxCLK
UCxCLK
UCxCLK
UCxSIMO/
UCxSOMI
UCxSIMO
UCxSOMI
Move to UCxTXBUF
RX Sample Points
0
1
0
0
0
1
1
1
0
X
1
X
MSB
MSB
1
2
3
4
5
6
7
8
LSB
LSB
TX Data Shifted Out
UCxSTE
UC
UC
eUSCI Operation – SPI Mode
940
SLAU356I – March 2015 – Revised June 2019
Copyright © 2015–2019, Texas Instruments Incorporated
Enhanced Universal Serial Communication Interface (eUSCI) – SPI Mode
Figure 25-4. eUSCI SPI Timing With UCMSB = 1
25.3.7 Using the SPI Mode With Low-Power Modes
The eUSCI module is not functional when the device is in the LPM3, LPM4, or LPMx.5 modes of
operation. However, the application can make use of the FORCE_LPM_ENTRY bit in the PCMCTL1
register to determine whether the entry to low-power mode should be aborted if the eUSCI is active, or if
the device can continue low power entry regardless. The latter option is useful if the eUSCI is transmitting
or receiving data at a very slow rate and the application should enter low-power mode at the expense of a
packet of data being lost. Refer to the
Power Control Manager (PCM)
chapter for more details.
25.3.8 SPI Interrupts
25.3.8.1 SPI Transmit Interrupt Operation
The UCTXIFG interrupt flag is set by the transmitter to indicate that UCxTXBUF is ready to accept another
character. An interrupt request is generated if UCTXIE is set. UCTXIFG is automatically reset if a
character is written to UCxTXBUF. UCTXIFG is set after a Hard Reset or when UCSWRST = 1. UCTXIE
is reset after a Hard Reset or when UCSWRST = 1.
NOTE:
Writing to UCxTXBUF in SPI mode
Data written to UCxTXBUF when UCTXIFG = 0 may result in erroneous data transmission.
25.3.8.2 SPI Receive Interrupt Operation
The UCRXIFG interrupt flag is set each time a character is received and loaded into UCxRXBUF. An
interrupt request is generated if UCRXIE is set. UCRXIFG and UCRXIE are reset by a Hard Reset or
when UCSWRST = 1. UCRXIFG is automatically reset when UCxRXBUF is read.