CHAPTER 10 SERIAL INTERFACE FUNCTION
User’s Manual U14492EJ3V0UD
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(4) Reception operation
An awaiting reception state is set by setting UARTCAE0 bit to 1 in the ASIM0 register and then setting RXE0
bit to 1 in the ASIM0 register. To start a receive operation, detect a start bit first. The start bit is detected by
sampling RXD0 pin. When the receive operation begins, serial data is stored sequentially in the reception
shift register according to the baud rate that was set. A reception completion interrupt (INTSR0) is generated
each time the reception of one frame of data is completed. Normally, the receive data is transferred from the
reception buffer register 0 (RXB0) to memory by this interrupt servicing.
(a) Reception enabled state
The receive operation is set to reception enabled state by setting the RXE0 bit in the ASIM0 register to 1.
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RXE0 bit = 1: Reception enabled state
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RXE0 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 0 (RXB0) are retained, and no reception completion interrupt or reception
error interrupt is generated.
(b) Start of reception operation
A reception operation is started by the detection of a start bit.
The RXD0 pin is sampled according to the serial clock from the baud rate generator 0 (BRG0).
(c) Reception completion interrupt
When RXE0 bit = 1 in the ASIM0 register and the reception of one frame of data is completed (the stop
bit is detected), a reception completion interrupt (INTSR0) is generated and the receive data within the
reception shift register is transferred to RXB0 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 0 (RXB0), and either a reception completion interrupt (INTSR0) or a reception error
interrupt (INTSER0) is generated according to the ISRM bit setting in the ASIM0 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 (INTSR0) or a reception error interrupt (INTSER0) is generated (the receive data within the
reception shift register is transferred to RXB0) according to the ISRM bit setting in the ASIM0 register.
If the RXE0 bit is reset (0) during a receive operation, the receive operation is immediately stopped. The
contents of the reception buffer register 0 (RXB0) and of the asynchronous serial interface status register
(ASIS0) at this time do not change, and no reception completion interrupt (INTSR0) or reception error
interrupt (INTSER0) is generated.
No reception completion interrupt is generated when RXE0 bit = 0 (reception is disabled).
Содержание V850E/IA1 mPD703116
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