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Data Communication circuit arrangements

Circuit Configuration:

Two point configuration

Multipoint configuration

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Data Communication Hardware

A multipoint data communication circuit block diagram

Primary Host

Secondary or remote

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Line control unit(LCU)

At Primary station :

provides interface between host computer and othercircuit.

At Secondary station:

Directs the flow of input and output data traffic betweenlinks and their application program.

It provides parallel to serial and serial to parallel conversionof data

LCU with a software is called as front end processor(FEP)

LCU has error detection and error correction.

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LCU operates only on digital data

Most of the functions of LCU are performed bysingle IC called as UART/USRT

UART- Universal asynchronous receiver/transmitter

USRT- Universal synchronous receiver/transmitter

INTELs USART 8251

Motorolas UART asynchronous communicationinterface adapter(ACIA)

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UART- Universal asynchronous receiver/transmitter

Asynchronous- no clocking information is transferred

between DTE and DCE

Primary functions of UART:

To perform serial to parallel and vice-versa

To perform error detection(parity bits)

To insert and detect start/stop bits

Hardware consists of 2 sections:Transmitter

receiver

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UART TRANSMITTER

TBMT-Transmit Buffer Empty

TD-Transmit Data

TDS-Transmit Data Strobe

TEOC-Transmit End of Char

TSO-Transmit serial out

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Control word

To indicate no of bits, nature of parity, and the

no of stop bits

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Receiver of UART

RSI-receive serial input

RDA-receive data available

RPE- receive parity error

SWE- status word enable

RDE-receive data enable

RDAR-receive data availablereset

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USRT- Universal synchronous

receiver/transmitter

Synchronous- clocking information is transferredbetween DTE and DCE

Primary functions of USRT:To perform serial to parallel and vice-versa

To perform error detection(parity bits)

To insert and detect SYN characters(differencebetween USRT& UART)

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Transceiver of USRTReceiver syn strobe

Transmitter syn strobeTCP- transmitter clock signal

SCR- syn character receive

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TBMT-Transmit Buffer Empty

TD-Transmit Data

TDS-Transmit Data Strobe

TEOC-Transmit End of Char

TSO-Transmit serial out

RSI-receive serial input

RDA-receive data available

RPE- receive parity error

SWE- status word enable

RDE-receive data enable

RDAR-receive data available reset

RR- Receive registerTCP- transmitter clock signal

RCP- Receiver clock signal

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Interfaces

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Serial Interface

Serial communication is the mostsimplistic form of communication between two devices.

RS-232 is a standard by which two serial devices communicate

The connection must be no longer than 50 feet.

Transmission voltages are15V and +15V. It is designed around transmission of characters(of 7 bits of length).

Defines a 25 wire cable with a DB 25S/9S connector.

Data rate of up-to 20kbps for a distance of 50ft

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Parallel interface

Transfers data between two devices eight or

more bits at a time.

Also referred to as serial by word transmission

advantage: faster transmission

Disadvantage: higher cost for transmission

Eg: Centronics parallel interface, IEEE 488 bus