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CHAPTER 14 SERIAL INTERFACE UART0
User
’
s Manual U14260EJ3V1UD
(d) Reception
The receive operation performs level detection.
The receive operation is enabled when 1 is set to bit 6 (RXE0) of asynchronous serial interface mode register
0 (ASIM0), and the input via the RxD0 pin is sampled.
The serial clock specified by baud rate generator control register 0 (BRGC0) is used to sample the RxD0
pin.
When the RxD0 pin goes low, the 5-bit counter of the baud rate generator begins counting and the start timing
signal for data sampling is output when half of the specified baud rate time has elapsed. If sampling the
RxD0 pin input at 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 recognized,
the character data, parity bit, and one-bit stop bit are detected, at which point reception of one data frame
is completed.
Once reception of one data frame is completed, the receive data in the shift register is transferred to receive
buffer register 0 (RXB0) and INTSR0 (receive completion interrupt request) occurs.
If the RXE0 bit is reset (to 0) during a receive operation, the receive operation is stopped immediately. At
this time, the contents of RXB0 and ASIS0 do not change, nor does INTSR0 or INTSER0 (receive error
interrupt request) occur.
Figure 14-11 shows the timing of the asynchronous serial interface receive completion interrupt request.
Figure 14-11. Timing of Asynchronous Serial Interface Receive Completion Interrupt Request
Caution
If the receive operation is enabled with the RxD0 pin input at the low level, the receive
operation is immediately started. Make sure the RxD0 pin input is at the high level before
enabling the receive operation.
RxD0 (input)
D0
D1
D2
D6
D7
Parity
Stop
Start
INTSR0