PixArt Imaging Inc.

PAC107

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37

PixArt Imaging Inc.

E-mail:

fae_service@pixart.com.tw

V1.4, Aug, 2005

Serial Port Signals

Function

Name

Type

Description

Multiplexed

With

TXD

O

Transmit Data.

In mode 0, TXD transmits the clock signal. In modes 1,

2,and 3,TXD transmits serial data.

P3.1

RXD

I/O

Receive Data.

In mode 0, RXD transmits and receives serial data. In

mode 1, 2,and 3, RXD receives serial data.

P3.0

Synchronous Mode (Mode 0)

Mode 0 is a half-duplex, synchronous mode, which is commonly used to expand I/O

capabilities of device with shift registers. The transmit data (TXD) pin outputs a set of

eight clock pulses which the receive data (RXD) pin transmits or receives a byte of data.

The transmission and reception are all least-significant bit (LSB) first. Shifts occurred in

the last phase (S6P2) of every peripheral cycle. Baud rate = Fosc/12.

Transmission (Mode 0)

Follow these steps to begin a transmission:

1.

Write to the SCON register, clearing bits SM0,SM1, and REN.

2.

Write 8-bit data to be transmitted to SBUF.

SUBF

(Transmit)

SCON

Write SBUF

Read SBUF

SUBF

(Receive)

Receive

Shift Register

Mode 0

Transmit

Load SBUF

Interrupt

Request

TI

RI

Serin I/O

Control

TXD

RXD

Serial Port Block Diagram

Transmit

shift Register