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ST90158 - SERIAL COMMUNICATIONS INTERFACE (SCI)

9.5 SERIAL COMMUNICATIONS INTERFACE (SCI)

9.5.1 Introduction

The Serial Communications Interface (SCI) offers

full-duplex serial data exchange with a wide range

of external equipment. The SCI offers four operat-

ing modes: Asynchronous, Asynchronous with

synchronous clock, Serial expansion and Syn-

chronous.

The SCI offers the following principal features:

Full duplex synchronous and asynchronous

operation.

Transmit, receive, line status, and device

address interrupt generation.

Integral Baud Rate Generator capable of

dividing the input clock by any value from 2 to

216-1 (16 bit word) and generating the internal

16X data sampling clock for asynchronous

operation or the 1X clock for synchronous

operation.

Fully programmable serial interface:

– 5, 6, 7, or 8 bit word length.

– Even, odd, or no parity generation and detec-

tion.

– 0, 1, 1.5, 2, 2.5, 3 stop bit generation.

– Complete status reporting capabilities.

– Line break generation and detection.

Programmable address indication bit (wake-up

bit) and user invisible compare logic to support

multiple microcomputer networking. Optional

character search function.

Internal diagnostic capabilities:

– Local loopback for communications link fault

isolation.

– Auto-echo for communications link fault isola-

tion.

Separate interrupt/DMA channels for transmit

and receive.

In addition, a Synchronous mode supports:

– High speed communication

– Possibility of hardware synchronization (RTS/

DCD signals).

– Programmable polarity and stand-by level for

data SIN/SOUT.

– Programmable active edge and stand-by level

for clocks CLKOUT/RXCL.

– Programmable active levels of RTS/DCD sig-

nals.

– Full Loop-Back and Auto-Echo modes for DA-

TA, CLOCKs and CONTROLs.

Figure 75. SCI Block Diagram

TRANSMIT

BUFFER

SHIFT

TRANSMIT

SHIFT

RECEIVER

FUNCTION

ALTERNATE

COMPARE

ADDRESS

BUFFER

RECEIVER

DMA

CONTROLLER

CLOCK and

BAUD RATE

GENERATOR

ST9 CORE BUS

SOUT

TXCLK/CLKOUT RXCLK

SIN

VA00169A

Frame Control

and STATUS

DMA

CONTROLLER

RTS

DCD

SDS

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