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Chapter 12
Serial Interface Function
Preliminary User’s Manual U14913EE1V0UM00
Figure 12-2: Asynchronous Serial Interface Mode Registers 0 to 2 (ASIM0 to ASIM2) (2/3)
Remark:
When reception is disabled, the reception shift register does not detect a start bit. No shift-in
processing or transfer processing to the reception buffer register (RXBn) is performed, and
the contents of the RXBn register are retained.
When reception is enabled, the reception shift operation starts, synchronized with the detec-
tion of the start bit, and when the reception of one frame is completed, the contents of the
reception shift register are transferred to the RXBn register. A reception completion interrupt
(INTSRn) is also generated in synchronization with the transfer to the RXBn register.
Bit Position
Bit Name
Function
5
RXE
Enables/disables reception.
0: Disable reception (Perform synchronous reset of reception circuit)
1: Enable
reception
Cautions: 1. Set the RXE bit to 1 after setting the CAE bit to 1 when
starting transfer. Set the CAE bit to 0 after setting the
RXE bit to 0 when stopping transfer.
2. To initialize the reception unit status, clear (0) the RXE
bit, and after letting 2 Clock cycles (base clock) elapse,
set (1) the RXE bit again. If the RXE bit is not set again,
initialization may not be successful. (For details about
the base clock, refer to 12.2.6 Dedicated baud rate gen-
erators 1 to 3 (BRG1 to BRG3).)
4, 3
PS1, PS0
Controls parity bit.
PS1
PS0
Transmit Operation
Receive Operation
0
0
Don’t output parity bit
Receive with no parity
0
1
Output 0 parity
Receive as 0 parity
1
0
Output odd parity
Judge as odd parity
1
1
Output even parity
Judge as even parity
Cautions: 1. To overwrite the PS1 and PS0 bits, first clear (0) the TXE
and RXE bits.
2. If “0 parity” is selected for reception, no parity judg-
ment is performed. Therefore, no error interrupt is gen-
erated because the PE bit of the ASISn register is not
set.
• Even parity
If the transmit data contains an odd number of bits with the value “1”, the
parity bit is set (1). If it contains an even number of bits with the value “1”,
the parity bit is cleared (0). This controls the number of bits with the value
“1” contained in the transmit data and the parity bit so that it is an even
number.
During reception, the number of bits with the value “1” contained in the
receive data and the parity bit is counted, and if the number is odd, a parity
error is generated.
•
Odd parity
In contrast to even parity, odd parity controls the number of bits with the
value “1” contained in the transmit data and the parity bit so that it is an odd
number. During reception, the number of bits with the value “1” contained in
the receive data and the parity bit is counted, and if the number is even, a
parity error is generated.
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