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Mnemonic
DO
CL
CR
VP
Function Monitored
Data Qut. On when data is transferred from this LANIC to the
Data Out AUI pair.
~ohlision
Detect. On when a collision is detected by the MAU
on this node. Since the MAU detects collisions whether it is
transmitting or not. the CL indicator comes on for every
collision that occurs on this coaxial cable. The CL indicator
does not come on when the MAU sends an SQE heartbeat after
transmission.
~aB.rier
Sense. On when data is detected coming into the node
on the Data In AUI pair. or on when the coJIision function is
detecting collisions. The CR indicator does not come on due to
SQE heartbeat.
'yoltage flus. This LED indicates the voltage present on this
12-volt supply lead to the MAU.
Principles of Operation
3-18
Each of the indicators for DO. CL. and CR consist of a pair of LEDs. labeled E
and
L.
The pair is driven in such a manner that all conditions of activity from
occasional isolated events to continuous events can be distinguished by the
unaided eye. This is accomplished in the following manner:
Each time that the event being monitored by an LED pair begins. the E LED
is turned on and remains on for 6 msec regardless of the length of the event.
The L LED turns on at the beginning of the event and turns off at the end of
the event.
Following this algorithm. a single isolated event of short duration produces a 6
msec blink of the E LED. and the L LED is on for the length of the event,
which is short. Therefore. the L LED appears to remain off.
As the frequency of events of short duration increases. the E LED appears to
be constantly lit. and the L LED begins to glow.
When short duration events occur constantly. both the
E
and
L
LEOs will
appear to be constantly lit.
A single event of very long duration produces a single 6 msec blink of the E
LED at the beginning of the event. and the L LED turns on and stays on for a
long time. until the event is completed.
Continuously occurring events of very long duration will cause the E LED to
blink at the beginning of each event for 6 msec. and the L LED will appear to
be constantly lit.
Events on a normally-operating network are all of short duration. For instance,
a maximum length frame requires only 1.2 msec to transmit; a minimum length
frame requires only 51 jJ.sec to transmit. Collisions have a maximum duration of
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