Contemporary Control Systems AI Active Hubs - Manual (Page 30)

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P1 and P2. These ports accommodate this signal generation
while maintaining compatibility with coaxial and fiber optic
signals.
3.1.3 Timers
A simple crystal oscillator and divider are used to develop the
unlatch delay time and reconfiguration timers. Although not
critical, the unlatch delay timer is more repeatable from a
crystal oscillator. However, the reconfiguration timer is more
critical. The reconfiguration timer does not sense a reconfigu-
ration on the network, it only predicts that a reconfiguration will
occur. This is accomplished by noting that no data has occurred
for 82
µ
s (at standard timeouts and at 2.5 Mbps). Once this
timer is exceeded, the yellow RECON LED is lit for about 950
ms. If the hub is operated on a network with extended ARCNET
timeouts, jumpers must be set on the timing module to extend
the reconfiguration timer to match the network timeouts. There
are a total of four jumper settings corresponding to the four
possible timeouts. Newer ARCNET controller chips allow for
adjustable reconfiguration timers beyond the original standards.
These settings could confuse the RECON LED. To disable the
RECON LED, simply remove any jumper attached to the four
timeout positions.
3.1.4 Watchdog Timer
If no hub activity is sensed after a predetermined time, a
watchdog timer will automatically reset the AI timing
electronics. This is to ensure that the AI reestablishes
communication after a significant electrostatic or
electromagnetic phenomenon without requiring any human
intervention.
3.2 LED Indicators
There are several LED indicators on the AI that aid in
determining if the network is operating correctly. The indicators
are as follows: