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Chapter 15
Serial Interface Channel UART
User’s Manual U16504EE1V1UD00
(d) Reception
The receive operation is enabled when bit 6 (RXE0) of the asynchronous serial interface mode
register (ASIM0) is set to "1", and input data via RXD pin is sampled.
The serial clock specified by ASIM0 is used when sampling the RXD pin.
When the RXD pin goes low, the 5-bit counter begins counting, the start timing signal for data
sampling is output if half of the specified baud rate time has elapsed. If the sampling of the RXD0
pin input of this start timing signal yields a low-level result, a start bit is recognized, after which the
5-bit counter is initialized and starts counting and data sampling begins. After the start bit is recog-
nized, the character data, parity bit, and one-bit stop bit are detected, at which point reception of
one data frame is completed.
Once the reception of one data frame is completed, the receive data in the shift register is trans-
ferred to the receive buffer register (RXB0) and a receive completion interrupt (INTSR0) occurs.
Even if an error has occurred, the receive data in which the error occurred is still transferred to
RXB0 and INTSR0 occurs (see Figure 14-9).
If the RXE0 bit is reset (to “0”) during a receive operation, the receive operation is stopped imme-
diately. At this time, neither the contents of RXB0 and ASIS0 will change, nor does INTSR0 or
INTSER0 occur.
Figure 15-12 shows the timing of the asynchronous serial interface receive completion interrupt.
Figure 15-12:
Timing of Asynchronous Serial Interface Receive Completion Interrupt
Caution:
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.
RXD (input)
D0
D1
D2
D6
D7
Parity
STOP
START
INTSR0