Measurement Computing CB-7011 - Manual (Page 62)

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CB-7011/CB-7011D, CD-7018 User’s Manual
3.3 Dual Watchdog Operation
Dual Watchdog = Module Watchdog + Host Watchdog
The Module Watchdog is a hardware reset circuit to moni-
tor the module’s operating status. While working in harsh or noisy
environment, the module may go down by the external noise signal.
The circuit may let the module continue to work and never halt.
The Host Watchdog is a software function to monitor the
host’s operating status. Its purpose is to prevent the network/com-
munication problem or a halted host from causing a dangerous
situation. While the timeout occurred, the module will place all out-
puts to the safe state to prevent from unexpected problem of con-
trolled target.
The CB-7000 module with Dual Watchdog makes the con-
trol system more reliable and stable.
3.4 Digital Input and Event Counter
The digital input DI0 can work as event counter. The counter
increments when the input changes from high level to low level.
The counter has 16 bits and is useful for low speed counting at
frequencies lower than 50 Hz.
3.5 Digital Output
When the module powers-on, the host watchdog timeout
flag is checked first. If the status is set, the digital outputs (DO0
and DO1) of module are set to the Safe Value. If the flag is clear,
the digital outputs are set to the Power-On Value.
If the host watchdog timeout flag is set, the module will