Delta RMC151 - Manual (Page 861)

8 Command Reference
• Use the Expression Editor to enter an expression in the Expression command. An
expression consists of tags, operators and functions. You can type directly into the
expression and also use the Expression Editor tabs to find the tags, operators and
functions you need. To insert an item from the Expression Builder, choose the item and
click Insert, or just double-click the item.
• If the expression consists of multiple lines, then each assignment statement must end
with a semicolon, as shown in the examples above.
For a full description of building expressions, see the Expressions Overview topic.
Data Types
Expressions follow a strict data type convention. If you mix data types in an expression,
you must use the type conversion functions. Note that "3" can be either a DINT or REAL
type, but "3.0" is only REAL type.
Order of Execution
Within a Step
Items in a step are always executed in order starting from the top. Therefore, the
Expression command is executed at the point it appears in a step in a user program. If
the Expression command assigns a value to a register, that register will take on that
value immediately. If that register is used in any following commands in the step, the
register will use the value that it was assigned.
Within the Expression Command
Statements in an Expression are executed in order starting from the top.
Logging Results
The RMC logs the results of assignments and copies in the Expression (113) command to
the Event Log for ease of troubleshooting. Logging does require significant processing
time. If your user programs exceed the allotted execution time, one method of reducing
the execution time is to disable expression logging. This will increase the amount of logic
that fits in each user program step.
To disable expression logging, in the Programming Properties dialog, in the Verify tab,
uncheck Log Expression Statements. With expression logging disabled, you can still
use the LOG_EVENT function to log specific items.
For more details on reducing user program execution time, see Program Capacity and
Time Usage.
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