NEC mPD789026 Subseries, User Manual

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CHAPTER 9 SERIAL INTERFACE 00
User's Manual U11919EJ3V0UM00
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(e) Receive errors
The following three errors may occur during a receive operation: a parity error, framing error, or
overrun error. Upon data reception, an error flag is set in asynchronous serial interface status register
00 (ASIS00). Receive error causes are shown in Table 9-7.
It is possible to determine what kind of error was generated during reception by reading the contents of
ASIS00 in the reception error interrupt servicing (see Figures 9-9 and 9-10).
The contents of ASIS00 are reset to 0 by reading receive buffer register 00 (RXB00) or receiving the
next data (if there is an error in the next data, the corresponding error flag is set).
Table 9-7. Receive Error Causes
Receive Error Cause
Parity error Transmission-time parity specification and reception data parity do not match
Framing error Stop bit not detected
Overrun error Reception of next data is completed before data is read from receive buffer register
Figure 9-10. Receive Error Timing
(a) Parity error generated
STOP
Parity D7 D6 D2 D1 D0
START
RxD (Input)
INTSR
(b) Framing error or overrun error generated
STOP
Parity D7 D6 D2 D1 D0
START
RxD (Input)
INTSR
Cautions 1. The contents of the ASIS00 register are reset to 0 by reading receive buffer register
00 (RXB00) or receiving the next data. To ascertain the error contents, read
ASIS00 before reading RXB00.
2. Be sure to read receive buffer register 00 (RXB00) even if a receive error is
generated. If RXB00 is not read, an overrun error will be generated when the next
data is received, and the receive error state will continue indefinitely.