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CHAPTER 14 SERIAL INTERFACE UART
(e) Receive errors
Three types of errors can occur during a receive operation: parity error, framing error, or overrun error. If,
as the result of data reception, an error flag is set to the asynchronous serial interface status register (ASIS),
a receive error interrupt (INTSER) will occur. Receive error interrupts are generated before receive interrupts
(INTSR). Table 14-4 lists the causes behind receive errors.
As part of receive error interrupt (INTSER) servicing, the contents of ASIS can be read to determine which
type of error occurred during the receive operation (see Table 14-4 and Figure 14-9).
The contents of ASIS are reset (to “0”) when the receive buffer register (RXB) is read or when the next data
is received (if the next data contains an error, another error flag will be set).
Table 14-4. Causes of Receive Errors
Receive Error
Cause
ASIS Value
Parity error
Parity specified during transmission does not match parity of receive data
04H
Framing error
Stop bit was not detected
02H
Overrun error
Reception of the next data was completed before data was read from the
01H
receive buffer register
Figure 14-9. Receive Error Timing
RxD (input)
D0
D1
D2
D6
D7
Parity
STOP
START
INTSR
Note
INTSER
(when framing/overrun
error occurs)
INTSER
(when parity error occurs)
Note If a reception error occurs when bit 1 (ISRM) of the asynchronous serial interface mode register
(ASIM) is set to 1, INTSR does not occur.
Cautions 1. The contents of asynchronous serial interface status register (ASIS) are reset (to
“0”) when the receive buffer register (RXB) is read or when the next data is received.
To obtain information about the error, be sure to read the contents of ASIS before
reading RXB.
2. Be sure to read the contents of the receive buffer register (RXB) even when a receive
error has occurred. Overrun errors will occur during the next data receive operations
and the receive error status will remain until the contents of RXB are read.
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