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CHAPTER 14 ASYNCHRONOUS SERIAL INTERFACE/3-WIRE SERIAL I/O
Note
To disable the reception completion interrupt when a reception error occurs, make sure that wait time
equivalent to two pulses of the clock that serves as the reference of the baud rate clock elapse after the
reception error occurs until the receive buffers (RXB, RXB2) are read. If the wait time is not inserted, the
reception completion interrupt occurs even when it is disabled.
The wait time equivalent to two pulses of the clock that serves as the reference of the baud rate clock can
be calculated by the following expression:
Wait time =
2
n+2
f
CLK
Remark
f
CLK
: Internal system clock frequency
n
: Value of baud rate generator control registers (BRGC, BRGC2) to select tap of 12-bit
prescaler (n = 0 to 11)
Caution An asynchronous serial interface mode register (ASIM/ASIM2) rewrite should not be performed
during a transmit operation. If an ASIM/ASIM2 register rewrite is performed during a transmit
operation, subsequent transmit operations may not be possible (normal operation is restored by
RESET input). Software can determine whether transmission is in progress by using a transmis-
sion completion interrupt (INTST/INTST2) or the interrupt request flag (STIF/STIF2) set by INTST/
INTST2.
(2) Asynchronous serial interface status register (ASIS), Asynchronous serial interface status register 2
(ASIS2)
The ASIS and ASIS2 contain flags that indicate the error contents when a receive error occurs. Flags are set (1)
when a receive error occurs, and cleared (0) when data is read from the receive buffer (RXB/RXB2). If the next data
is received before RXB/RXB2 is read, the overrun error flag (OVE/OVE2) is set (1), and the other error flags are
cleared (0) (if there is an error in the next data, the corresponding error flag is set (1)).
These registers can be read only by an 8-bitmanipulation instruction or bit manipulation instruction. The format of
ASIS and ASIS2 is shown in Figure 14-4.
These registers are cleared to 00H by RESET input.