ST72340 datasheet(99/191 Pages) STMICROELECTRONICS

99 / 191 page

ST72340, ST72344, ST72345

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11.5 SCI SERIAL COMMUNICATION INTERFACE

11.5.1 Introduction

The Serial Communications Interface (SCI) offers

a flexible means of full-duplex data exchange with

external equipment requiring an industry standard

NRZ asynchronous serial data format. The SCI of-

fers a very wide range of baud rates using two

baud rate generator systems.

11.5.2 Main Features

■ Full duplex, asynchronous communications

■ NRZ standard format (Mark/Space)

■ Dual baud rate generator systems

■ Independently

programmable

transmit

and

receive baud rates up to 500K baud

■ Programmable data word length (8 or 9 bits)

■ Receive buffer full, Transmit buffer empty and

End of Transmission flags

■ 2 receiver wake-up modes:

– Address bit (MSB)

– Idle line

■ Muting function for multiprocessor configurations

■ Separate

enable bits for Transmitter and

Receiver

■ 4 error detection flags:

– Overrun error

– Noise error

– Frame error

– Parity error

■ 5 interrupt sources with flags:

– Transmit data register empty

– Transmission complete

– Receive data register full

– Idle line received

– Overrun error detected

■ Parity control:

– Transmits parity bit

– Checks parity of received data byte

■ Reduced power consumption mode

11.5.3 General Description

The interface is externally connected to another

device by three pins (see Figure 1). Any SCI bidi-

rectional communication requires a minimum of

two pins: Receive Data In (RDI) and Transmit Data

Out (TDO):

– SCLK: Transmitter clock output. This pin outputs

the transmitter data clock for synchronous trans-

mission (no clock pulses on start bit and stop bit,

and a software option to send a clock pulse on

the last data bit). This can be used to control pe-

ripherals that have shift registers (e.g. LCD driv-

ers). The clock phase and polarity are software

programmable.

– TDO: Transmit Data Output. When the transmit-

ter is disabled, the output pin returns to its I/O

port configuration. When the transmitter is ena-

bled and nothing is to be transmitted, the TDO

pin is at high level.

– RDI: Receive Data Input is the serial data input.

Oversampling techniques are used for data re-

covery by discriminating between valid incoming

data and noise.

Through these pins, serial data is transmitted and

received as frames comprising:

– An Idle Line prior to transmission or reception

– A start bit

– A data word (8 or 9 bits) least significant bit first

– A Stop bit indicating that the frame is complete.

This interface uses two types of baud rate generator:

– A conventional type for commonly-used baud

rates,

– An extended type with a prescaler offering a very

wide range of baud rates even with non-standard

oscillator frequencies.

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