Do Led Pair - HP 30242 Installation And Service Manual

Principles of Operation
CR CaRrier Sense. On when data is detected coming into the node on
the Data In AUI pair, or on when the collision function is
detecting collisions. The CR indicator does not come on due to SQE
heartbeat.
VP ~oltage Plus. This LED indicates the voltage present on this
12-volt supply lead to the MAU.
Each of the indicators for DO, CL, and CR consist of a pair of LEOs, 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 lJ,sec to transmit.
Collisions have a maximum duration of only
49
USec. For events of short duration such as these, the
E
and
L
LEOs can be visualized as a sort of two-column bar graph. Frequency of activity is increasing as
the frequency of flashing of the E LED increases while the L LED is off or very dim. When the E LED
is always on, the
L
LED indicates further increase in activity by becoming brighter and brighter until it
reaches full intensity. This state of the E and L LEOs indicates continuous short events.
To understand the indications given by the DO, CL, and CR LEOs, it is necessary to understand how the
signals that drive these LEOs are related to the signals on the AUI cable.
DO LED PAIR. The event indicated by the DO LED pair is the enabling of the data encoder by the
protocol controller on the LANIC. The event begins when the encoder is turned on. While the encoder is
on, a continuous stream of encoded data bits is transmitted by the LANIC to the DO AUI pair. The event
ends when the data encoder is disabled. When the encoder is disabled, data bits are no longer sent to the
DO pair. The transmission of a single frame to the AUI DO pair is one event, and will cause the E LED
to blink on for 6 msec. The
L
LED will be lit for the length of time required to transmit the data bits to
the AUI pair, a maximum of
1. 2
msec for a maximum length frame.
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