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USART Operation: SPI Mode
15-12 USART Peripheral Interface, SPI Mode
SPI Receive Interrupt Operation
The URXIFGx interrupt flag is set each time a character is received and loaded
into UxRXBUF as shown in Figure 15−11 and Figure 15−12. 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 or when UxRXBUF is
read.
Figure 15−11.Receive Interrupt Operation
URXS
Clear
τ
(S)
SYNC
Valid Start Bit
Receiver Collects Character
URXSE
From URXD
PE
FE
BRK
URXEIE
URXWIE
RXWAKE
Character Received
URXIFGx
URXIEx
Interrupt Service
Requested
SWRST
PUC
UxRXBUF Read
URXSE
IRQA
SYNC = 1
Clear
Figure 15−12. Receive Interrupt State Diagram
Receive
Character
Completed
Interrupt
Service Started,
GIE = 0
URXIFGx = 0
USPIEx = 0
URXIFGx = 1
USPIEx = 1 and
URXIEx = 1 and
GIE = 1 and
Priority Valid
GIE = 0
Priority
Too
Low
URXIFGx = 0
Wait For Next
Start
USPIEx = 0
SWRST = 1
PUC
USPIEx = 1
URXIEx = 0
SWRST = 1
Receive
Character