
259
μPD780948, μPD78F0948, μPD780949, μPD78F0949
(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 the data reception, an error flag is set to the asynchronous serial interface status register
(ASIS0), a receive error interrupt (INTSER) will occur. Receive error interrupts are generated before receive
interrupts (INTSR). Table 17-5 lists the causes behind receive errors.
As part of receive error interrupt (INTSER) servicing, the contents of ASIS0 can be read to determine
which type of error occurred during the receive operation (see Table 17-5 and Figure 17-13).
The content of ASIS0 is reset (to “0”) if the receive buffer register (RXB0) is read or when the next data
is received (if the next data contains an error, another error flag will be set).
Table 17-5: Causes of Receive Errors
Receive error
Cause
ASIS0 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
receive buffer register
01H
Figure 17-13: Receive Error Timing
Cautions:
1. The contents of ASIS0 are reset (to “0”) when the receive buffer register (RXB0) is
read or when the next data is received. To obtain information about the error, be sure
to read the contents of ASIS0 before reading RXB0.
2. Be sure to read the contents of the receive buffer register (RXB0) 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 RXB0 are read.
RxD0 (input)
D0
D1
D2
D6
D7
Parity
STOP
START
INTSR0
INTSER0
INTSER0
(When parity error occurs)