Nexto XF – #43 Using Special Variables

The objective of this tutorial is to explain how to use special variables in a MasterTool X project.

Components

Equipment: 1 computer/notebook.

Software: MasterTool X

Tutorial Sections

1. ARCHITECTURE
2. DEVELOPMENT

1. ARCHITECTURE

A computer/notebook will be required to use MasterTool X.

Figure 1. Computer running MasterTool X

2. DEVELOPMENT

Special variables are variables automatically created by the system, used to provide internal PLC information or ready-to-use signals in the logic, such as periodic pulses and time and date data.

These variables:

• Are predefined by the system
• Are global
• Can be used anywhere in the project
• Are organized in the project tree

Where to find the Special Variables

Special variables are located in the project tree in:

System GVLs - (System Global Variable Lists)

Within this folder, the user will find:

• Pulsating variables (clock/pulse)
• Variables related to the RTC (Real Time Clock)

Because they are global, it is not necessary to declare them in any POU or in UserPrg; simply use them directly in the logic.

Figure 2. Special Variables Menu

Pulsating Variables

Pulsating variables are signals automatically generated by the PLC, with periodic behavior, very useful for:

• Signaling flashes
• Simple timings
• Logic tests
• Generation of cyclical events without the use of timers

Example: Pulse_2s variable

Despite the name Pulse_2s, it is important to understand its operation correctly.

This variable does not stay on for 2 seconds and then off for 2 seconds.

It generates a square wave, that is:

• 1 second at TRUE level (on)
• 1 second at FALSE level (off)

Totaling a period of 2 seconds.

This behavior is typical of a square wave, where the on time is equal to the off time.

RTC (Real-Time Clock) Variables

The variables related to the RTC (Real-Time Clock) provide information such as:

• Year
• Month
• Day
• Hour
• Minute
• Second
• Day of the week

Important note about the RTC

RTC variables only function correctly when used in physical equipment.

In simulation mode:

• There is no real synchronization with an internal clock
• The values ​​may not reflect the actual time behavior

Correct synchronization depends on the PLC's internal clock, which exists only in the physical hardware.

Typical Applications of RTC Variables

• Time-based logic
• Scheduling
• Daily counters
• Event logging
• Date and time-dependent systems

Figure 3. Operation of special variables

Practical example in UserPrg

In UserPrg, a pulsed variable can be used directly as a contact:

• Insert a normally open contact
• Assign the variable pulse2s
• Connect this contact to a coil

Operation:

• Every 1 second the coil turns on
• In the following second the coil turns off
• The cycle repeats continuously while the PLC is in RUN

This feature eliminates the need to use a TON block just to blink an output.

Figure 4. Use of special variables in UserPrg logic

Advantages of using Special Variables

• They do not require declaration
• They are global
• They reduce the use of timers and counters
• They facilitate testing and diagnostics
• They increase the clarity of the logic

Final observation

Whenever possible:

• Use pulsed variables for simple timing logic
• Use RTC only in environments with a physical PLC
• Avoid recreating solutions that the system itself already provides in an optimized way

This feature makes the code cleaner, more efficient, and easier to maintain.