Technical data

Programming with STEP 7
Manual, 05/2010, A5E02789666-01 441
20 Testing with the Variable Table
20.1 Introduction to Testing with Variable Tables
Variable tables offer the advantage of being able to store various test environments. Thus, tests
and monitoring can be effortlessly reproduced during operation or for the purpose of service and
maintenance. There is no limit to the number of variable tables that can be stored.
When testing using variable tables, the following functions are available:
• Monitoring Variables
This function enables you to display on the programming device/PC the current values of
individual variables in a user program or a CPU.
• Modifying Variables
You can use this function to assign fixed values to individual variables of a user program or a
CPU. Modifying values once and immediately is also possible when testing using program
status.
• Enable Peripheral Output and Activate Modify Values
These two functions allow you to assign fixed values to individual I/O outputs of a CPU in
STOP mode.
• Forcing Variables
You can use this function to assign individual variables of a user program or a CPU with a fixed
value that cannot be overwritten by the user program.
You can assign or display the values for the following variables:
• Inputs, outputs, bit memory, timers, and counters
• Contents of data blocks
• I/O (periphery)
You enter the variables you want to display or modify in variable tables.
You can determine when and how often the variables are monitored or assigned new values by
defining a trigger point and trigger frequency.