beautypg.com

4 transmit-interrupt operation, Figure 13–14. transmit-interrupt operation – Texas Instruments MSP430x1xx User Manual

Page 260

background image

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.