Attention

IronPLC can only run very simple programs. The steps described are accurate but many language features are not yet supported.

I/O Qualifiers¶

Direct representation allows variables to be mapped to specific locations in the process image using address prefixes.

IEC 61131-3	Section 2.4.1.1
Support	Partial

Address Prefixes¶

Prefix	Region	Description
`%I`	Input	Read from physical inputs
`%Q`	Output	Write to physical outputs
`%M`	Memory	Internal memory (markers)

Size Prefixes¶

Prefix	Size	Description
`X`	1 bit	Single bit (default)
`B`	8 bits	Byte
`W`	16 bits	Word
`D`	32 bits	Double word
`L`	64 bits	Long word

Syntax¶

variable_name AT %prefix.address : type_name ;

Example¶

PROGRAM main
    VAR
        start_button AT %IX0.0 : BOOL;
        motor_output AT %QX0.0 : BOOL;
        speed_setpoint AT %MW10 : INT;
    END_VAR

    motor_output := start_button;
END_PROGRAM

See Also¶

Variable Declarations — basic variable declarations
Variable Scope — variable scope keywords