CR16MCS5 datasheet(72/156 Pages) NSC

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flag is automatically reset when software reads the character

from the UnRBUF register. The RSFT register is not user ac-

cessible.

18.2.2

Synchronous Mode

The synchronous mode of the USART enables the device to

communicate with other devices using three communication

signals: transmit, receive, and clock. In this mode, data bits

are transferred synchronously with the USART clock signal.

Data bits are transmitted on the rising edges and received on

the falling edges of the clock signal, as shown in Figure34.

Data bytes are transmitted and received least significant bit

(LSB) first.

In the synchronous mode, the transmit shift register (TSFT)

and the transmit buffer (UnTBUF) double-buffer the data for

transmission. To transmit a character, a data byte is loaded

in the UnTBUF register. The data is then transferred to the

TSFT register. The TSFT register shifts out one bit of the cur-

rent character, LSB first, on each rising edge of the clock.

Figure 32.

USART Block Diagram

Sys_clk

Baud clock

Baud Clock

TDXn

RDXn

Transmitter

Receiver

Baud Rate Generator

Control and

Error Detection

Parity

Generator/Checker

CKXn

Figure 33.

USART Asynchronous Communication

Sample

STARTBIT

DATA (LSB)

Sample

DATABIT

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