Under “Data Files” select “S2: Status” to display the status memory of the PLC. Look through and notice many of the values that are available. The values that are gray can only be written to, while the others can be set by on the screen or by a ladder logic program. Also notice that memory addresses are also provided.
Enter the following ladder logic. Notice that the first scan value ‘S2:1/15” has been recognized as the first pass value. Download and run the program. Turn off the PLC and repeat. Notice how the bit is only set when the PLC is turned on.
- Go to “Database” then “Address/Symbol” and double click. This will bring up a list of labels for all of the IO points in the system, including those defined by the user, and predefined values such as status bits.