Contemporary Control Systems EXP Expansion Modules User Manual - Manual (Page 27)

accommodate this signal generation while maintaining
compatibility with coaxial and fiber optic signals.
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
reconfiguration 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). 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.
Watchdog Timer
If no hub activity is sensed after a predetermined time, a
watchdog timer will automatically reset the MOD HUB timing
module. This is to ensure that the hub reestablishes
communication after a significant electrostatic or
electromagnetic phenomenon without requiring any human
intervention.
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