Texas Instruments MSP430x4xx Family, Руководство пользователя

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USCI Operation: UART Mode
19-25 Universal Serial Communication Interface, UART Mode
19.3.14 Using the USCI Module in UART Mode with Low-Power Modes
The USCI module provides automatic clock activation for SMCLK for use with
low-power modes. When SMCLK is the USCI clock source, and is inactive
because the device is in a low-power mode, the USCI module automatically
activates it when needed, regardless of the control-bit settings for the clock
source. The clock remains active until the USCI module returns to its idle
condition. After the USCI module returns to the idle condition, control of the
clock source reverts to the settings of its control bits. Automatic clock activation
is not provided for ACLK.
When the USCI module activates an inactive clock source, the clock source
becomes active for the whole device and any peripheral configured to use the
clock source may be affected. For example, a timer using SMCLK will
increment while the USCI module forces SMCLK active.
19.3.15 USCI Interrupts
The USCI has one interrupt vector for transmission and one interrupt vector
for reception.
USCI Transmit Interrupt Operation
The UCAxTXIFG interrupt flag is set by the transmitter to indicate that
UCAxTXBUF is ready to accept another character. An interrupt request is
generated if UCAxTXIE and GIE are also set. UCAxTXIFG is automatically
reset if a character is written to UCAxTXBUF.
UCAxTXIFG is set after a PUC or when UCSWRST = 1. UCAxTXIE is reset
after a PUC or when UCSWRST = 1.
USCI Receive Interrupt Operation
The UCAxRXIFG interrupt flag is set each time a character is received and
loaded into UCAxRXBUF. An interrupt request is generated if UCAxRXIE and
GIE are also set. UCAxRXIFG and UCAxRXIE are reset by a system reset
PUC signal or when UCSWRST = 1. UCAxRXIFG is automatically reset when
UCAxRXBUF is read.
Additional interrupt control features include:
-
When UCAxRXEIE = 0 erroneous characters will not set UCAxRXIFG.
-
When UCDORM = 1, non-address characters will not set UCAxRXIFG in
multiprocessor modes. In plain UART mode no characters will set
UCAxRXIFG.
-
When UCBRKIE = 1 a break condition will set the UCBRK bit and the
UCAxRXIFG flag.