TLF7405

May 1988

DP8392ANS32492A Coaxial Transceiver Interface

General Description

The DP8392A Coaxial Transceiver Interface (CTI) is a coax-

ial cable line driverreceiver for EthernetThin Ethernet

(Cheapernet) type local area networks The CTI is connect-

ed between the coaxial cable and the Data Terminal Equip-

ment (DTE) In Ethernet applications the transceiver is usu-

ally mounted within a dedicated enclosure and is connected

to the DTE via a transceiver cable In Cheapernet applica-

tions the CTI is typically located within the DTE and con-

nects to the DTE through isolation transformers only The

CTI consists of a Receiver Transmitter Collision Detector

and a Jabber Timer The Transmitter connects directly to a

50 ohm coaxial cable where it is used to drive the coax

when transmitting During transmission a jabber timer is ini-

tiated to disable the CTI transmitter in the event of a longer

than legal length data packet Collision Detection circuitry

monitors the signals on the coax to determine the presence

of colliding packets and signals the DTE in the event of a

collision

The CTI is part of a three chip set that implements the com-

plete IEEE 8023 compatible network node electronics as

shown below The other two chips are the DP8391 Serial

Network Interface (SNI) and the DP8390 Network Interface

Controller (NIC)

The SNI provides the Manchester encoding and decoding

functions whereas the NIC handles the Media Access Pro-

tocol and the buffer management tasks Isolation between

the CTI and the SNI is an IEEE 8023 requirement that can

be easily satisfied on signal lines using a set of pulse trans-

formers that come in a standard DIP However the power

isolation for the CTI is done by DC-to-DC conversion

through a power transformer

Features

Y

Compatible with Ethernet II IEEE 8023 10Base5 and

10Base2 (Cheapernet)

Y

Integrates all transceiver electronics except signal

power isolation

Y

Innovative design minimizes external component count

Y

Jabber timer function integrated on chip

Y

Externally selectable CD Heartbeat allows operation

with IEEE 8023 compatible repeaters

Y

Precision circuitry implements receive mode collision

detection

Y

Squelch circuitry at all inputs rejects noise

Y

Designed

for

rigorous

reliability

requirements

of

IEEE 8023

Y

Standard Outline 16-pin DIP uses a special leadframe

that significantly reduces the operating die temperature

Table of Contents

10

System Diagram

20

Block Diagram

30

Functional Description

31

Receiver and Squelch

32

Transmitter and Squelch

33

Collision and Heartbeat

34

Jabber Timer

40

Connection Diagram

50

Pin Descriptions

60

Absolute Maximum Ratings

70

Electrical Characteristics

80

Switching Characteristics

90

Timing and Load Diagram

100 Physical Dimensions

10 System Diagram

TLF7405 – 1

IEEE 8023 Compatible EthernetCheapernet Local Area Network Chip Set

C1995 National Semiconductor Corporation

RRD-B30M105Printed in U S A