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Chapter 13
Serial Interface Function
Preliminary User’s Manual U15839EE1V0UM00
(4)
Receive operation
An awaiting reception state is set by setting Power bit to 1 in the ASIMn register and then setting
RXE bit to 1 in the ASIMn register. To start a receive operation, detects a start bit first. The start bit
is detected by sampling RXD5n pin. When the receive operation begins, serial data is stored
sequential in the reception shift register according to the baud rate that was set. A reception
completion interrupt (INTSRn) is generated each time the reception of one frame of data is
completed. Normally, the receive data is transferred from the reception buffer register (RXBn) to
memory by this interrupt servicing (n = 0, 1).
(a) Reception enabled state
The receive operation is set to reception enabled state by setting the RXE bit in the ASIM0 register
to 1.
• RXE bit = 1: Reception enabled state
• RXE bit = 0: Reception disabled state
In reception disabled state, the reception hardware stands by in the initial state. At this time, the
contents of the reception buffer register (RXBn) are retained, and no reception completion
interrupt or reception error interrupt is generated.
(b) Starting a receive operation
A receive operation is started by the detection of a start bit.
The RXDn pin is sampled according to the serial clock from the dedicated baud rate generator
(BRG) of UART5n (n = 0, 1).
(c) Reception completion interrupt
When RXE bit = 1 in the ASIMn register and the reception of one frame of data is completed (the
stop bit is detected), a reception completion interrupt (INTSRn) is generated and the receive data
within the reception shift register is transferred to RXBn at the same time.
Also, if an overrun error (OVE) occurs, the receive data at that time is not transferred to the
reception buffer register (RXBn), and either a reception completion interrupt (INTSRn) or a
reception error interrupt (INTSERn) is generated (the receive data within the reception shift
register is transferred to RXBn) according to the ISRM bit setting in the ASIMn register.
Even if a parity error (PE) or framing error (FE) occurs during a reception operation, the receive
operation continues until stop bit is received, and after reception is completed, either a reception
completion interrupt (INTSRn) or a reception error interrupt (INTSERn) is generated according to
the ISRM bit setting in the ASIMn register.
If the RXE bit is reset (0) during a receive operation, the receive operation is immediately stopped.
The contents of the reception buffer register (RXBn) and of the asynchronous serial interface
status register (ASISn) at this time do not change, and no reception completion interrupt (INTSRn)
or reception error interrupt (INTSERn) is generated.
No reception completion interrupt is generated when RXE bit = 0 (reception is disabled).
Figure 13-11:
Asynchronous Serial Interface Reception Completion Interrupt Timing
Start
D0
D1
D2
D6
D7
RXD5n (input)
INTSR5n (output)
RXB5n register
Parity
Stop
Содержание mPD703128
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