How to Program a Quantum Hot Standby Application

Processor Configuration

There are two types of MAST task execution modes:

Cyclic - The MAST task executes as rapidly as possible.
Periodic - The MAST task delays execution (if necessary) to observe a user-defined minimum cycle time.

When the periodic mode is used, the user-defined period must take into account the longer mast task periods necessary in a redundant system.

The following table presents the characteristics of MAST tasks that may be adjusted by the user in Control Expert:

Characteristics	Control Expert Default Values
Max period (ms)	255
Default period (ms)	20 (Note: Set to 80 ms as an initial value for Hot Standby systems)
Min. period (ms)	1 (0 if the Cyclic MAST task execution mode is selected)
Period increment (ms)	1
Max Watchdog (ms)	1500
Default Watchdog (ms)	250
Min. Watchdog (ms)	10

For more details, see Adjusting Mast Task Properties.

Detecting Cold and Warm Starts of a Quantum Hot Standby PLC

In a Quantum Hot Standby PLC, only the System Word %SW10 and the System Bit %S1 can be used to detect respectively a Cold Start and a Warm Start.

%SW10 (Cold-start test):

If the value of the %SW10.0 bit (representing the MAST task) is set to 0, this means that the task is performing its first cycle after a Cold Start.

At the end of the first cycle of the MAST task, the system sets the bit %SW10.0 to 1.
%S1 (Warm-start test):

The default value of %S1 Is 0. This bit is set to 1 when the device power is cycled and a data save operation is performed. If this value is 1, this is an indication that the last start performed was a Warm Start.

It is reset to 0 by the system at the end of the first complete cycle, but before the outputs are updated.

To process your application based on the type of start, the program must test whether %SW10.0 is reset to 0 (or %S1 is set to 1) at the start of first MAST task. %SW10 and %S1 can be tested by the application in either the Primary or Standby mode.