NEC PD78214 - Manual (Page 279)

250
µ
PD78214 Sub-Series
Table 9-1 Causes of Reception Errors
Parity error
Framing error
Overrun error
The parity of the receive data does not match the type of parity specified at transmission.
No stop bit is detected Note .
Before the receive data is read out from the reception buffer, the next data is received.
Cause Reception error
★
Note Reception assumes that only one stop bit is used. Therefore, if the transmission end uses a two-stop bit format, and the second stop
bit is low when received, no reception error is detected; it is recognized as the start bit of the next data.
Fig. 9-7 Reception Error Timing
STOP
D6 Parity D7 D2 D1 D0
START
RxD (Input)
INTSR
INTSER
Remark With the µPD78214, no break signal can be detected by hardware. Because a break signal consists of two characters’ worth of low
level, software identifies it by detecting that a framing error has occurred twice consecutively where the receive data is 00H. Software
can differentiate the break signal from a sequence of two accidental framing errors. This is done by reading the level of the RxD pin
(by reading port 3 (P3) by setting bit 0 of the port 3 mode register to 1) and checking if it is 0.
Cautions 1. The ASIS register is reset to 0 when the reception buffer (RXB) is read-accessed or receives the next data. To identify the error,
be sure to check the ASIS before reading data from the RXB. If a macro service is used during reception, it is impossible to
identify the error; it is only possible to know an error has occurred (an INTSER has occurred or the reception error interrupt
request flag (SERIF) is set to 1). Make sure that this poses no problem for your application.
2. Be sure to read the reception buffer (RXB) contents, even if a reception error occurs. Otherwise, an overrun error will occur when
the next data is received, and the error status will persist.