FINAL
Publication# 07506 Rev: EAmendment/0
Issue Date: May 1994
1

Am7996

IEEE 802.3/Ethernet/Cheapernet Transceiver

DISTINCTIVE CHARACTERISTICS

n

Compatible with Ethernet Version 2 and
IEEE 802.3 10BASE-5and10BASE-2
specifications

n

Pin-selectable SQE Test (heartbeat) option

n

Internal jabber controller prevents excessive
transmission time

n

Noise rejection filter ensures that only valid data
is transmitted onto the network

n

Collision detection on both transmit and receive
data

n

Collision detect threshold levels adjustable for
other networking applications

GENERAL DESCRIPTION

The Am7996 IEEE 802.3/Ethernet/Cheapernet Trans-
ceiver supports Ethernet Version 2, IEEE 802.3
10BASE-5 and IEEE 802.3 10BASE-2—Cheapernet)
transceiver applications. Transmit, receive, and colli-
sion detect functions at the coaxial media interface to
the data terminal equipment (DTE) are all performed by
this single device.
In an IEEE 802.3 (10BASE-5)/Ethernet application, the
Am7996 interfaces the coaxial (0.4

†

diameter) media to the
DTE through an isolating pulse transformer and the 78

W

attachment unit interface (AUI) cable. In IEEE 802.3
10BASE-2—Cheapernet applications, the Am7996 typi-
cally resides inside the DTE with its signals to the DTE iso-
lated and the coaxial (0.2

†

diameter) media directly
connected to the DTE. Transceiver power and ground in
both applications are isolated from that of the DTE.
The Am7996’s tap driver provides controlled skew and
current drive for data signaling onto the media. The jabber
controller prevents the node from transmitting exces-
sively. While transmitting, collisions on the media are de-
tected if one or more additional stations are transmitting.
The Am7996 features an optional SQE Test function
that provides a signal on the Cl pair at the end of every
transmission. The SQE Test indicates the operational
status of the Cl pair to the DTE. It can also serve as an
acknowledgment to the node that packet transmission
onto the coax was completed.

BLOCK DIAGRAM
Line
Driver
Line
Driver
Transmit
Data
Amplifier
Control
Logic
Carrier
Detect
Circuit
Receive
Data
Amplifier
Collision
Detect
Circuit
Jabber
Timer
SQE Test
Generator
Transmit
Squelch
Input
Buffer
SQE TEST
AUI Interface
DO+
DO–
Control
Logic
Tap
Driver
TXT
Coaxial Media Interface
Input
Buffer
CI+
CI–
DI+
DI–
RXT
07506E-1