You can use diagnostic parameters in expressions to check the integrity and status of specific devices. Using the diagnostic parameters in expressions, you can perform error handling and react to unexpected conditions. For example, you could use a condition block and write an expression that checks the status of an I/O card. If the status is bad, you could execute a different control strategy. The expression for checking the status of an IO card would look similar to the following:
'//CTLR1/IO1/C02/STATUS' != GOOD;
Note
As a general guideline, for parameters with a numeric value, the status is GOOD if it is zero. For Boolean parameters, FALSE is a GOOD status, and TRUE indicates an error.
For a numeric value, the expression would look similar to the following:
'//CTLR1/IO1/C02/CH02/STATUS' = 0;