Texas Instruments MSP430x1xx - Manual (Page 260)

Interrupt and Control Functions
13-14
13.4.4 Transmit-Interrupt Operation
In the transmit-interrupt operation shown in Figure 13–14, the transmit-
interrupt flag UTXIFG is set by the transmitter to indicate that the transmitter
buffer UTXBUF is ready to accept another character. This bit is automatically
reset if the interrupt-request service is started or a character is written to the
UTXBUF. This flag activates a transmitter interrupt if bits USPIE and GIE are
set. The UTXIFG is set after a system reset PUC signal, or removal of SWRST.
Figure 13–14. Transmit-Interrupt Operation
Clear
USPIE
Clear
D
Character Moved From
Buffer to Shift Register
Request_
Interrupt_Service
SWRST
UTXBUF Written Into Transmit Shift Register
Q
UTXIFG
IRQA
VCC
PUC or SWRST
Q
Set
SYNC = 1
The transmit-interrupt enable bit UTXIE controls the ability of the UTXIFG to
request an interrupt, but does not prevent the UTXIFG flag from being set. The
USPIE is reset with a PUC signal or a SWRST. The UTXIFG bit is set after a
system reset PUC signal or a SWRST, but the USPIE bit is reset to ensure full
interrupt-control capability.