3. Theory of Operation
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•
The end of the AUI cable opposite the MAU connects to a latching, 15-pin,
subminiature "D" connector (
J2
) the front of the ZT 8995. The slide latch retention
system found on J2 meets IEEE 802.3 requirements.
Thin Ethernet (BNC) Connector
As an alternative to the Ethernet AUI connector, Thin Ethernet (Cheapernet) uses
smaller and less expensive BNC coax (RG58A/U). It connects to a BNC connector at
the front of the ZT 8995 (
J1
). Normally a BNC "T" connector is attached to the BNC
connector so that two RG58 A/U cables may be attached at this point. If the ZT 8995 is
the first or last board on the network cable, the unused "T" connector is fitted with a 50
ohm (±2%) termination cap.
The on-board DP8392 coaxial transceiver interface connects the network interface
controller to the Thin Ethernet cable. This circuitry replaces the MAU typically used to
interface with the Ethernet cable. No external transceiver cable (AUI) is necessary
because the DP8392 includes isolation transformers and uses a DC/DC converter.
DIAGNOSTIC LEDS
The ZT 8995 interface has separate transmit and receive diagnostic LEDs. These LEDs
provide visual indication of network activity. Transmit activity is indicated by a red LED
in the center of the LED block. Receive activity is indicated by the lowest green LED.
The red transmit indicator LED lights when the ZT 8995 sends a packet. Receive
indicators (typically green) are illuminated on remaining interfaces while this occurs.
The green receive indicator LED lights when the interface detects any packet present
on the cable. Detection is indicated when a packet is transmitted from the ZT 8995 or
when other interfaces on the network transmit information. The packet need not be
intended for the ZT 8995.
Additional LEDs are used to indicate proper cable link, polarity, and collisions. The LED
sequence on the board from top (nearest the ejector) to bottom is as follows:
RED - polarity, illuminates if the twisted pair cable has inverted polarity
GREEN - link indicator, illuminates when a properly connected cable is detected
RED - Transmit, illuminates when the ZT 8995 transmits an information packet
GREEN - Receive, illuminates whenever a packet of information is detected on the
network
RED - Collision, illuminates when a transmitted packet collides with another on the
network
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