FINAL
Publication# 03378 Rev: I Amendment/0
Issue Date: May 1993
1

Am7992B

Serial Interface Adapter (SIA)

DISTINCTIVE CHARACTERISTICS

n

Compatible with lEEE 802.3/Ethernet/Cheapernet
specifications

n

Crystal/TTL oscillator-controlled Manchester
encoder

n

Manchester decoder acquires clock and data
within four bit times with an accuracy of

–

3 ns

n

Guaranteed carrier and collision detection
squelch threshold limits

—Carrier/collision detected for inputs greater than
–275 mV
—No carrier/collision for inputs less than –175 mV

n

Input signal conditioning rejects transient noise

—Transients <10 ns for collision detector inputs
—Transients <20 ns for carrier detector inputs

n

Receiver decodes Manchester data with worst
case

–

19 ns of clock jitter (at 10 MHz)

n

TTL-compatible host interface

n

Transmit accuracy +0.01% (without adjustments)

GENERAL DESCRIPTION

The Am7992B Serial Interface Adapter (SIA) is a
Manchester encoder/decoder compatible with IEEE
802.3, Cheapernet, and Ethernet specifications. In an
IEEE 802.3/Ethernet application, the Am7992B inter-
faces the Am7990 Local Area Network Controller for
Ethernet (LANCE) to the Ethernet transceiver device,
acquires clock and data within four bit times, and de-
codes Manchester data with worst case

–

19 ns phase
jitter at 10 MHz. SIA provides both guaranteed signal
threshold limits and transient noise suppression cir-
cuitry in both data and collision paths to minimize false
start conditions.

BLOCK DIAGRAM
03378I-1
Manchester
Decoder
Data
Receiver
Noise
Reject
Filter
Carrier
Detect
Noise
Reject
Filter
Collision
Detect
Manchester
Encoder
Crystal
OSC
Receive Data (RX)
Receive Clock (RCLK)
Carrier Present (RENA)
Collision (CLSN)
Transmit Data (TX)
Transmit Enable (TENA)
Transmit Clock (TCLK)
20 MHz
XTAL
1
XTAL
2
Receive+
Receive–
Collision+
Transmit+
Transmit–
Collision–
Controller Interf
ace
T
r
ansceiv
er Interf
ace