Collision Detection - HP 30240A Installation And Service Manual

Collision Detection
off. The LANIC is informed of the shut-off condition by a continuous signal
(SQE) on the CI pair of the AUI cable. The MAU is prevented from
transmitting until 500 milliseconds after the Jabber Fault is removed.
When a collision occurs on the coaxial cable. the DC voltage on the cable
increases in magnitude and the collision detection circuitry senses this condition.
The LANIC is informed of this condition by a signal sent from the MAU on the
CONTROL IN (CI) cable pair (part of the AUI cable). The collision detection
scheme employed implements receiver-based collision detection. This means that
the presence of two or more transmitters can be detected even when the MA U is
not transmitting.
To insure that the collision detection circuitry is working satisfactorily. it is
tested each time a data packet is sent. At the end of each transmitted packet. a
'Heartbeat', or SEQ (Signal Quality Error) test signal (which is a short burst of the
collision indicator signal) is sent to the LANIC.
Receiver
To/F
rom Coaxial
Cable
-(
Transmitter
-
)
t
T
ofF
rom Lanic
Jabber
Detection
Circuitry
t
Collision
Detection
Circuitry
Figure 3-4. MAU Functional Block Diagram
Principles of Operation
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