NEC PD78F9488 - Manual (Page 208)

CHAPTER 11 SERIAL INTERFACE 20
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User’s Manual U15331EJ4V1UD
(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 11-7.
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 Table 11-7 and Figure 11-10).
The contents of ASIS20 are reset (0) by reading receive 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 11-7. Receive Error Causes
Receive Errors Receive Errors Value of ASIS20
Parity error Parity at transmission and reception do not match 04H
Framing error Stop bit not detected 02H
Overrun error Reception of next data is completed before data is read from receive buffer
register 01H
Figure 11-10. Receive Error Timing
(a) Parity error occurrence
STOP
Parity D7 D6 D2 D1 D0
START
RxD20 (input)
INTSR20
(b) Framing error or overrun error occurrence
STOP
Parity D7 D6 D2 D1 D0
START
RxD20 (input)
INTSR20
Cautions 1. The contents of the ASIS20 register are reset (0) by reading receive buffer register
20 (RXB20) or receiving the next data. To ascertain the error contents, read ASIS20
before reading RXB20.
2. Be sure to read receive 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.