HD6417618 datasheet(396/646 Pages) RENESAS

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Section 14 Serial Communication Interface with FIFO (SCIF)

Rev. 6.00 Jun. 12, 2007 Page 364 of 610

REJ09B0131-0600

14.4.2

Operation in Asynchronous Mode

In asynchronous mode, each transmitted or received character begins with a start bit and ends with

a stop bit. Serial communication is synchronized one character at a time.

The transmitting and receiving sections of the SCIF are independent, so full duplex

communication is possible. The transmitter and receiver are 16-byte FIFO buffered, so data can be

written and read while transmitting and receiving are in progress, enabling continuous transmitting

and receiving.

Figure 14.2 shows the general format of asynchronous serial communication. In asynchronous

serial communication, the communication line is normally held in the mark (high) state. The SCIF

monitors the line and starts serial communication when the line goes to the space (low) state,

indicating a start bit. One serial character consists of a start bit (low), data (LSB first), parity bit

(high or low), and stop bit (high), in that order.

When receiving in asynchronous mode, the SCIF synchronizes at the falling edge of the start bit.

The SCIF samples each data bit on the eighth pulse of a clock with a frequency 16 times the bit

rate. Receive data is latched at the center of each bit.

LSB

Start

bit

MSB

Idle state

(mark state)

Stop bit

Transmit/receive data

0/1

Serial

data

Parity

bit

1 bit

1 or 2 bits

7 or 8 bits

1 bit or

none

One unit of transfer data (character or frame)

Figure 14.2 Example of Data Format in Asynchronous Communication

(8-Bit Data with Parity and Two Stop Bits)

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