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CHAPTER 11 SERIAL INTERFACE
147
(d) Reception
When bit 6 (RXE00) of asynchronous serial interface mode register 00 (ASIM00) is set to 1, a receive
operation is enabled and sampling of the RxD00 pin input is performed.
RxD00 pin input sampling is performed using the serial clock specified by ASIM00.
When the RxD00 pin input becomes low, the 5-bit counter of the baud rate generator starts counting,
and at the time when the half time determined by the specified baud rate has passed, the data sampling
start timing signal is output. If the RxD00 pin input sampled again as a result of this start timing signal
is low, it is identified as a start bit, the 5-bit counter is initialized and starts counting, and data sampling
is performed. When character data, a parity bit, and one stop bit are detected after the start bit,
reception of one frame of data ends.
When one frame of data has been received, the reception data in the shift register is transferred to
reception buffer register 00 (RXB00), and a reception completion interrupt request (INTSR00) is
generated.
Even if an error is generated, the reception data in which the error was generated is still transferred to
RXB00. If bit 1 (ISRM00) of ASIM00 is cleared to 0 when an error is generated, INTSR00 is generated
(see Figure 11-9). If the ISRM00 bit is set to 1, INTSR00 is not generated.
If the RXE00 bit is cleared to 0 during the receive operation, the receive operation is stopped
immediately. In this case, the contents of RXB00 and ASIS00 are not changed, and INTSR00 and
INTSER00 are not generated.
Figure 11-8 shows the asynchronous serial interface reception completion interrupt request timing.
Figure 11-8. Asynchronous Serial Interface Reception Completion Interrupt Request Timing
Caution
Be sure to read reception buffer register 00 (RXB00) even if a receive error occurs. 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.
STOP
Parity
D7
D6
D2
D1
D0
START
RxD00 (Input)
INTSR00