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 interfaces the Am7990 Local Area Network Controller for Ethernet (LANCE) to the Ethernet transceiver device, acquires clock and data within four bit times, and decodes Manchester data with worst case ±19 ns phase jitter at 10 MHz.SIA provides both guaranteed signal threshold limits and transient noise suppression circuitry in both data and collision paths to minimize false

start conditions.

DISTINCTIVE CHARACTERISTICS

■Compatible with lEEE 802.3/Ethernet/Cheapernet specifications

■Crystal/TTL oscillator-controlled Manchester encoder

■Manchester decoder acquires clock and data within four bit times with an accuracy of ±3 ns

■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

■Input signal conditioning rejects transient noise

   —Transients <10 ns for collision detector inputs

   —Transients <20 ns for carrier detector inputs

■Receiver decodes Manchester data with worst case ±19 ns of clock jitter (at 10 MHz)

■TTL-compatible host interface

■Transmit accuracy +0.01% (without adjustments)