Delta AH500 series Manual download pdf (Page 33)

AH500 Quick Start

VAR_INPUT

When the program is executed, the value of the external variable is brought into the internal variable.

If the value of the corresponding internal variable is altered, it is not transmitted to the external

variable. VAR_INPUT is often used if the value of the external variable should not be modified. Most

of inputs in this example are digital inputs, and these inputs should not be modified. The modification

of the values of these variables affects the execution of the program or the use of the function block.

In order to prevent the values of these variables from being modified in the program, the declaration

type should be VAR_INPUT.

VAR_IN_OUT

When the program is executed, the value of the external variable is brought into the internal variable.

After the program comes to an end, the value is transmitted to the external variable. VAR_IN_OUT

is often used if the value of the variable should be modified. Generally speaking, Pump_Auto and

Pump_Man_SW in this example are used in the SCADA system to set the control mode of the pump.

It seems that VAR_INPUT meets the need. However, users need to switch the control mode of the

pump from the automatic mode to the manual mode to stop the command from being outputted

when the pump trips. Therefore, the declaration type for these two variables should be

VAR_IN_OUT.

VAR_OUTPUT

When the program is executed, the value of the external variable is not brought into the internal

variable, but the value memorized before is used instead. After the program comes to an end, the

value is transmitted to the external variable. Generally speaking, the variable appears at the output

of the instruction.

VAR

When the program is executed, VAR is regarded as an internal variable, and the value memorized

before is used. Generally speaking, the variable is used as a register when it is used in the program.

If the same variable (function block type) is assigned to the function blocks which are called many

times in the program, the initial value of VAR_OUTPUT and that of VAR are not necessarily the

same as those used last time.

Users can create the local symbols as follows.

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Delta AH500 series Manual Page 33