CHAPTER 12 SERIAL INTERFACE 20
(e) Receive errors
The following three errors may occur during a receive operation: a parity error, framing error, and
overrun error. After data reception, an error flag is set in asynchronous serial interface status register
20 (ASIS20). Receive error causes are shown in Table 12-7.
It is possible to determine what kind of error occurred during reception by reading the contents of
ASIS20 in the reception error interrupt servicing (see Figures 12-9 and 12-10).
The contents of ASIS20 are reset (0) by reading reception buffer register 20 (RXB20) or receiving the
next data (if there is an error in the next data, the corresponding error flag is set).
Table 12-7. Receive Error Causes
Receive Errors
Cause
Transmission-time parity and reception data parity do not match
Stop bit not detected
Parity error
Framing error
Overrun error
Reception of next data is completed before data is read from reception buffer register
Figure 12-10. Receive Error Timing
(a) Parity error occurrence
STOP
D0
D1
D2
D6
D7
Parity
RxD20 (input)
START
INTSR20
(b) Framing error or overrun error occurrence
STOP
D0
D1
D2
D6
D7
Parity
RxD20 (input)
INTSR20
START
Cautions 1. The contents of the ASIS20 register are reset (0) by reading reception buffer
register 20 (RXB20) or receiving the next data. To ascertain the error contents,
read ASIS20 before reading RXB20.
2. Be sure to read reception buffer register 20 (RXB20) even if a receive error occurs.
If RXB20 is not read, an overrun error will occur when the next data is received,
and the receive error state will continue indefinitely.
User’s Manual U15075EJ1V0UM00
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NEC [ NEC ]
