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USART Operation: UART Mode
14-18 USART Peripheral Interface, UART Mode
USART Receive Interrupt Operation
The URXIFGx interrupt flag is set each time a character is received and loaded
into UxRXBUF. An interrupt request is generated if URXIEx and GIE are also
set. URXIFGx and URXIEx are reset by a system reset PUC signal or when
SWRST = 1. URXIFGx is automatically reset if the pending interrupt is served
(when URXSE = 0) or when UxRXBUF is read. The operation is shown in
Figure 14−11.
Figure 14−11.Receive Interrupt Operation
Clear
URXS
Clear
τ
S
SYNC
Valid Start Bit
Receiver Collects Character
URXSE
From URXD
PE
FE
BRK
URXEIE
URXWIE
RXWAKE
Erroneous Character Rejection
Non-Address Character Rejection
Character Received
or
Break Detected
URXIFGx
URXIEx
Interrupt Service
Requested
SWRST
PUC
UxRXBUF Read
URXSE
IRQA
S
URXEIE is used to enable or disable erroneous characters from setting
URXIFGx. When using multiprocessor addressing modes, URXWIE is used
to auto-detect valid address characters and reject unwanted data characters.
Two types of characters do not set URXIFGx:
- Erroneous characters when URXEIE = 0
- Non-address characters when URXWIE = 1
When URXEIE = 1 a break condition will set the BRK bit and the URXIFGx flag.