ST72E121 datasheet(50/92 Pages) STMICROELECTRONICS

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ST72E121 ST72T121

4.4 SERIAL COMMUNICATIONS INTERFACE (SCI)

4.4.1 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.

4.4.2 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 250K baud.

Programmable data word length (8 or 9 bits)

Receive buffer full, Transmit buffer empty and

End of Transmission flags

Two receiver wake-up modes:

– Address bit (MSB)

– Idle line

Muting function for multiprocessor configurations

Separate

enable bits for Transmitter and

Receiver

Three error detection flags:

– Overrun error

– Noise error

– Frame error

Five interrupt sources with flags:

– Transmit data register empty

– Transmission complete

– Receive data register full

– Idle line received

– Overrun error detected

4.4.3 General Description

The interface is externally connected to another

device by two pins (see Figure 33):

– 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 this pins, serial data is transmitted and re-

ceived 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 usestwo 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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