Measurement Computing CB-COM-7012 - Manual (Page 67)

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CB-7012, CB-7014, CB-7017 User’s Manual
3.3 Dual Watchdog Operation
Dual Watchdog = Module Watchdog + Host Watchdog
The Module Watchdog is a hardware reset circuit used to
monitor the module’s operating status. When working in an electri-
cally noisy environment, the module may go down from a noise
signal. The outputs go to the PowerOn Value. The module can
accept the host’s command to change the output value.
The Host Watchdog is a software function to monitor the
host’s operating status. Its purpose is to detect a network/
communication problem or a halted host. If a timeout occurs, the
module will place all outputs to their Safe Value to prevent any
problem in the controlled unit/process.
The CB-7000 module with Dual Watchdog makes the
control system safer and more reliable.
3.4 Digital Input and Event Counter
The digital input DI0 can work as an event counter. The
counter updates when the input changes from a high level to a low
level. The counter is 16 bits wide and useful for low speed counting
at frequencies lower than 50 Hz.
3.5 Digital Output
When the module is powered on, the host watchdog timeout
status is checked first. If the status is set, the digital outputs (DO0
and DO1) of module are set to the Safe Value. If the status is clear,
the digital outputs are set to the PowerOn Value.
If the host watchdog timeout status is set, the module will