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CHAPTER 13 SERIAL INTERFACE UART
Preliminary User’s Manual U14581EJ3V0UM00
(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 interrupt
requests (INTSR). Table 13-4 lists the causes behind receive errors.
As part of receive error interrupt servicing (INTSER), the contents of ASIS can be read to determine which
type of error occurred during the receive operation (see Table 13-4 and Figure 13-9).
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 13-4. 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 13-9. 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 ISRM bit 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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