How do you define the "TRUE" constant in the LAD/FDB editor in STEP 7 (TIA Portal)?

Entry ID:87149213 Date:2014-02-03

STEP 7 (TIA Portal) -- Creating S7 programs -- Addressing variables and data structures

S7-1200 CPU 12xx -- Creating S7 programs -- Addressing variables and data structures

S7-1500 CPU 15xx -- Creating S7 programs -- Addressing variables and data structures

How do you define the "TRUE" constant in the LAD/FDB editor in STEP 7 (TIA Portal)?

Description You can only set the "TRUE" constant for binary links for the S7-300/S7-400 in the STL programming language, but not in the LAD/FDB editor. For this you must set a variable to "1" (=TRUE) in the LAD and FBD programming languages. Then you can use the variable with its given value in any network of the program.

Option 1: Set variable to TRUE Fig. 01 gives an example of how to set the "Always_True" variable always to "1". For this you can also use any other variable in the program that now always has the value "TRUE".

Fig. 01

Option 2: Define system memory In the S7-1200/S7-1500 you can define the system memory in the device configuration. System memories are memories with defined values.

1. Open the device configuration of your S7-1200/S7-1500 CPU and in the navigation area you click "System and clock memory".

2. Enable the "Enable the use of system memory byte" option. 3. Assign a number for the "Address of system memory byte". The default value "1" is entered

here. 4. Save and compile your program.

The example below (Fig. 02) the system memory byte is defined as "1". The M1.2 variable then always has the value "TRUE".

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Fig. 02

Note The selected memory byte cannot be used for buffering.

Note on the Programming Guidelines for S7-1200/1500 Since the system memory and the clock memory depend on the hardware we recommend that you follow the programming guidelines for programming and configuring the S7-1200/S7-1500. More information about the programming guidelines is available in Entry ID: 81318674.

Creation environment The screens in this FAQ response were created with STEP 7 (TIA Portal) V12.

Entry ID:87149213 Date:2014-02-03

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