Texas Instruments MSP430x4xx - Manual (Page 297)

USART Operation: SPI Mode
15-11 USART Peripheral Interface, SPI Mode
15.2.6 SPI Interrupts
The USART has one interrupt vector for transmission and one interrupt vector
for reception.
SPI Transmit Interrupt Operation
The UTXIFGx interrupt flag is set by the transmitter to indicate that UxTXBUF
is ready to accept another character. An interrupt request is generated if
UTXIEx and GIE are also set. UTXIFGx is automatically reset if the interrupt
request is serviced or if a character is written to UxTXBUF.
UTXIFGx is set after a PUC or when SWRST = 1. UTXIEx is reset after a PUC
or when SWRST = 1. The operation is shown is Figure 15−10.
Figure 15−10. Transmit Interrupt Operation
Clear
UTXIEx
Clear
D
Character Moved From
Buffer to Shift Register
Interrupt Service Requested
SWRST
Data moved to UxTXBUF
Q
UTXIFGx
IRQA
V
CC
PUC or SWRST
Q
Set
SYNC = 1
Note: Writing to UxTXBUF in SPI Mode
Data written to UxTXBUF when UTXIFGx = 0 and USPIEx = 1 may result in
erroneous data transmission.