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 1511 and Figure 1512. 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 1511.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 1512. 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