CHAPTER 12 SERIAL INTERFACE FUNCTION
Preliminary User’s Manual U15905EJ1V0UD
317
(4) Receive operation
The awaiting reception state is set by setting the UARTCAEn bit to 1 in the ASIMn register and then setting the
RXEn bit to 1 in the ASIMn register. To start the receive operation, first perform start bit detection. The start
bit is detected by sampling the RXDn pin. When the receive operation begins, serial data is stored
sequentially in the receive 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 receive buffer register n (RXBn) to memory by this interrupt servicing.
(a) Reception enabled state
The receive operation is set to the reception enabled state by setting the RXEn bit in the ASIMn register to
1.
•
RXEn bit = 1: Reception enabled state
•
RXEn bit = 0: Reception disabled state
In reception disabled state, the reception hardware stands by in the initial state. At this time, the contents
of receive buffer register n (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 using the serial clock from baud rate generator n (BRGn).
(c) Reception completion interrupt
When RXEn = 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 receive
shift register is transferred to RXBn at the same time.
Also, if an overrun error (OVEn) occurs, the receive data at that time is not transferred to receive buffer
register n (RXBn), and either a reception completion interrupt (INTSRn) or a reception error interrupt
(INTSREn) is generated (the receive data within the receive shift register is transferred to RXBn)
according to the ISRMn bit setting in the ASIMn register.
Even if a parity error (PEn) or framing error (FEn) 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 (INTSREn) is generated according to the ISRM
bit setting in the ASIMn register.
If the RXEn bit is reset (0) during a receive operation, the receive operation is immediately stopped. The
contents of receive buffer register n (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 (INTSREn) is generated.
No reception completion interrupt is generated when RXEn = 0 (reception is disabled).
Содержание V850ES/SA2 UPD703201
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