What is a system variable?¶
A system variable is a symbol in the symbol table that provides specific information. The content of these variables is provided by the Grafcet engine.
Use of system variables:¶
Examples with system variables:
- Let an output blink with 1 Hz
- Switch something on or off depending on the time of day
- Time measurements: if a step is active for too long, then react to it or program your own timers.
Below you will find concrete examples.
How to use a system variable?¶
First you insert the system variable into the symbol table and then you can use it like any other symbol. All system variables can be inserted in the symbol table via the context menu. Then simply delete the symbols you do not need.
In the following animated GIF file you can see how to insert the system variables. Variables that are not required are then deleted.
Which system variables are available?¶
Table System Variables:
|System variable||Data type||Description|
|_SI_RTC_YEAR||UInt16||Returns the current year|
|_SI_RTC_MONTH||Byte||Returns the current month|
|_SI_RTC_DAY||Byte||Returns the current day|
|_SI_RTC_H||Byte||Returns the current hour|
|_SI_RTC_M||Byte||Returns the current minute|
|_SI_RTC_S||Byte||Returns the current second|
|_SI_RTC_MS||UInt16||Returns the current millisecond|
|_SI_TOGGLE||Bool||Changes with every cycle: True, False, True, ...|
|_SI_1HZ||Bool||Delivers a 1 Hz clock pulse (e.g. for signal lamps)|
|_SI_10HZ||Bool||Delivers a 10 Hz clock pulse. Maybe the cycle time may not be adequate to deliver a 10 Hz clock. Available in version 18.104.22.168 or newer.|
|_SI_100HZ||Bool||Delivers a 100 Hz clock pulse. Maybe the cycle time may not be adequate to deliver a 100 Hz clock. Available in version 22.214.171.124 or newer.|
|_SI_TICKS||UInt32||Is a millisecond counter. Time measurements possible|
|_SI_CYCLIC_COUNTER||UInt16||Is always incremented by 1 during each cycle.|
|_SI_CYCLIC_TIME||UInt16||Returns the current cycle time in milliseconds|
|_SI_VERSION||UInt16||Returns the current Grafcet Engine version|
|_SI_WBYTES||UInt16||If >0, then the monitoring/watch mode of Grafcet-Studio is active|
Example: Let an output blink at 1 Hz
Example: Switch on the output at 12:00 and switch it off again at 13:00. The following picture shows 2 variants:
Example: If a step is active for more than 5 seconds, switch the output 'TimeOut' to '1'.
Download examples as a Grafcet-Studio project file System-Variables-Examples
Grafcet-Studio version 126.96.36.199 or newer required