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DO LED Pair
CL LED Pair
CR LED Pair
only 49
}.lsec.
For events of short duration such as these, the E and L LEDs 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. \Vhen 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 LEDs indicates continuous short events.
To understand the indications given by the DO. CL. and CR LEDs. it is necessary
to understand how the signals that drive these LEDs are related to the signals on
the AUI cable.
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 dat.a bits is
transmitted by the LANIC to the DO AVI 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 A VI 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.
The event indicated by the CL LED pair is the occurrence of the Signal Quality
Error (Collision) signal on the Control In pair of the
AVI
cable. When t.he
MAV. whether it is transmitting to the coaxial cable or not. detects a collision on
the cable. it sends the SQE signal to the LANIC on the CI pair. SQE is signalled
by a 10 MHz signal on the CI pair. The event begins when the first transition is
received at the LANIC. and ends 200 nsec after the last transition is received.
The SQE heartbeat. which is a short burst of 10 MHz signal on the CI pair after
each transmission by the LANIC on DO. does not cause the E LED to blink.
although it does cause the
L
LED to light for approximately I j..lsec. which is too
short to be seen. Likewise, no collision occurring on the network within 5.3
}.lsec
of cessation of transmission by the LANIC will light the
E
LED. The SQE
heartbeat is blocked from triggering the
E
LED so that the CL LEOs will
indicate the frequency of collisions occurring on the network.
The event indicated by the CR LED pair is the reception of data on the Data In
pair in the AUI cable. or the occurrence of the collision event described above.
The event begins when the first data transition arrives on the A
VI
DI pair. or
when the collision event begins. whichever occurs first. The event ends 200 nsec
after the last data transition on the DI pair. or when the collision event ends.
whichever occurs last.
Principles of Operation
3-19
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