Chapter 6 Symbol Variables VAR － General symbol The symbols of this class are for general operations only. The significance of a symbol of this class depends on the data type of the symbol or the corresponding device. VAR_RETAIN - Latched symbol When symbol variable is declared as VAR_RETAIN, it will automatically be configured in retain latched area. Therefore, when PLC host is latched, the symbol variables retains its value. VAR_STATIC － Static symbol With static attributes, a symbol of this class is used only when defining the variables in POU (Program organization units). A static variable will be given a fixed address so as to share the same value across different instances.
VAR_STATIC RETAIN － Static-retained symbol Variables declared as static and retained would still keep the latest values after a power failure of PLC device. VAR_INPUT － Symbol variable for function block input terminal point A symbol of this class is used as an input terminal point in a function block. If a function block is called, the symbol of this class can receive the input value from the caller. In ladder or function block editing environment, the VAR_INPUT is arranged on the left side of the function block diagram and will configure one terminal point to receive the input value of the caller.
VAR_OUTPUT － Symbol variable for function block input terminal point A symbol of this class is used as an output terminal point in a function block. After the execution of a function block is complete, the operation result will be sent to the caller through the symbol of this class. In ladder or function block editing environment, the VAR_OUTPUT is arranged on the right side of the function block diagram and will configure one terminal point to receive the input value of the caller. VAR_IN_OUT － Symbol variable for feedback terminal point A symbol of this class is used as a feedback terminal point in a function block. Please refer to the following example.
When the function block is called, the caller sends the value in D1 to DT_IO, which is a symbol of the VAR_IN_OUT class. After the operation comes to an end, the final value of DT_IO is sent to D1. In ladder or function block editing environment, the VAR_IN_OUT is arranged on the left side of the function block diagram and the terminal point is in blue bold lines used to connect with the caller. 6-5