Measurement Computing CB-7000 DIO - Manual (Page 58)

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CB-7000 DIO Manual
3.3 Dual Watchdog Operation
Dual Watchdog = Module Watchdog + Host Watchdog
The Module Watchdog is a hardware reset circuit that
monitors the module’s operating status. When working in harsh or
noisy environment, the module may go down by a noise signal. The
Module Watchdog times out and sets output to PowerOn value.
The Host Watchdog is a software function to monitor the
host’s operating status. Its purpose is to detect a network communi-
cation problem or a halted host. When the timeout interval expired,
the module will put all outputs to the predefined Safe Value. This
places the controlled element in a known-safe condition.
The CB-7000 module with Dual Watchdog makes the
control system more reliable and stable.
3.4 Reset Status
The Reset Status is set while the module power on or reset
by Module Watchdog, and is cleared when the Command read
Reset Status ($AA5) is applied. This is useful for user to check the
module’s working status. When the Reset Status is set means the
module is reset and the output may be changed to the PowerOn
Value. When the Reset Status is clear means the module is not
reset, and the output cannot be changed.
3.5 Digital Output
A module’s output can have one of three values:
1. Safe Value. If the host watchdog timeout status is set,
the output is set to Safe Value.If the module receives an output