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ASYNCHRONOUS SERIAL COMMUNICATIONS INTERFACE (SCI-A)

10.6 ASYNCHRONOUS SERIAL COMMUNICATIONS INTERFACE (SCI-A)

10.6.1 Introduction

The Asynchronous Serial Communications Inter-

face (SCI-A) offers a flexible means of full-duplex

data exchange with external equipment requiring

an industry standard NRZ asynchronous serial

data format. The SCI-A offers a very wide range of

baud rates using two baud rate generator sys-

tems.

10.6.2 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 700K 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

■ Parity control:

– Transmits parity bit

– Checks parity of received data byte

■ Reduced power consumption mode

■ LIN Master: 13-bit LIN Synch Break generation

capability

10.6.3 General Description

The interface is externally connected to another

device by two pins (see Figure 118):

– TDO: Transmit Data Output. When the trans-

mitter is disabled, the output pin is in high im-

pedance. When the transmitter is enabled and

nothing is to be transmitted, the TDO pin is at

high level.

– RDI: Receive Data Input is the serial data in-

put. Oversampling techniques are used for

data recovery 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 com-

plete.

This interface uses two types of baud rate genera-

tors:

– 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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