GENERAL DESCRIPTION
The Integrated Multiport Repeater Plus (IMR+) chip is a VLSI circuit that provides a system-level solution to designing a compliant 802.3 repeater incorporating 10BASE-T transceivers. The device integrates the Repeater functions specified by Section 9 of the IEEE 802.3 standard and Twisted-Pair Transceiver functions complying with the 10BASE-T standard. The Am79C981 provides eight integral twisted-pair medium attachment units (MAUs) and an attachment unit interface (AUI) port in an 84-pin plastic leaded chip carrier (PLCC).

DISTINCTIVE CHARACTERISTICS
■ Enhanced version of AMD’s Am79C980 Integrated Multiport Repeater™ (IMR™) chip with the following enhancements:
   — Additional management port features
   — Minimum mode provides support for an extra four LED outputs per port for additional status in non-intelligent repeater designs
   — Pin/socket-compatible with the Am79C980 IMR chip
   — Fully backward-compatible with existing IMR device designs
■ Interfaces directly with the Am79C987 HIMIB™ device to build a fully managed multiport repeater
■ CMOS device features high integration and low power with a single +5 V supply
■ Repeater functions comply with IEEE 802.3 Repeater Unit specifications
■ Eight integral 10BASE-T transceivers utilize the required predistortion transmission technique
■ Attachment unit interface (AUI) port allows connectivity with 10BASE-5 (Ethernet) and 10BASE-2 (Cheapernet) networks, as well as 10BASE-F and/or Fiber Optic Inter-Repeater Link (FOIRL) segments
■ On-board PLL, Manchester encoder/decoder, and FIFO
■ Expandable to increase number of repeater ports
■ All ports can be separately isolated (partitioned) in response to excessive collision conditions or fault conditions
■ Network management and optional features are accessible through a dedicated serial management port
■ Twisted-pair Link Test capability conforming to the 10BASE-T standard.The receive Link Test function can be optionally disabled through the management port to facilitate interoperability with devices that do not implement the LinkTest function
■ Programmable option of Automatic Polarity Detection and Correction permits automatic recovery due to wiring errors
■ Full amplitude and timing regeneration for retransmitted waveforms
■ Preamble loss effects eliminated by deep FIFO