Swap Byte (SWPB)

This information applies to the

CompactLogix

5370,

ControlLogix

5570,

Compact GuardLogix

5370,

GuardLogix

5570,

Compact GuardLogix

5380,

CompactLogix

5380,

CompactLogix

5480,

ControlLogix

5580, and

GuardLogix

5580 controllers.

The SWPB instruction rearranges the order of the bytes of the Source. It places the result in the Destination.

Available Languages

Ladder Diagram

Function Block

This instruction is not available in function block.

Structured Text

SWPB(Source, Order Mode, Dest);

Operands

IMPORTANT:

Unexpected operation may occur if:

Output tag operands are overwritten.

Members of a structure operand are overwritten.

Except when specified, structure operands are shared by multiple instructions.

There are data conversion rules for mixing numeric data types within an instruction. See Data Conversion
.

Ladder Diagram and Structured Text

Operand	Data Type	Format	Description
Source	INT DINT	tag	Tag that contains the bytes to rearrange.
Order Mode		list item	This operand specifies how to reorder. Refer Order Mode table.
Dest	INT DINT	tag	Tag to store the bytes in a new order. Refer Dest table.

If selecting the HIGH/LOW order mode, enter it as HIGHLOW (without the slash). See Structured Text Syntax for more information on the syntax of expressions within structured text.

Order Mode

If the Source is an	And you want to change the bytes to this pattern(each letter represents a different byte)	Then select
INT	AB => BA	Any option
DINT	ABCD => DCBA	REVERSE
	ABCD =>CDAB	WORD
	ABCD => BADC	HIGH/LOW

Dest

If the Source is an	Then the Destination must be an
INT	INT, DINT If the destination is a DINT, the result is sign extended after bytes swap.
DINT	DINT

Affects Math Status Flags

Major/Minor Faults

None specific to this instruction. See Index Through Arrays for array-indexing faults.

Execution

Ladder Diagram

Condition/State	Action Taken
Prescan	N/A
Rung-condition-in is false	N/A
Rung-condition-in is true	The instruction rearranges the specified bytes.
Postscan	N/A

Structured Text

Condition/State	Action Taken
Prescan	See Prescan in the Ladder Diagram table.
Normal Execution	See Rung-condition-in is true in the Ladder Diagram table.
Postscan	See Postscan in the Ladder Diagram table.

Examples

Example 1 - Swap the bytes of a DINT tag

The three SWPB instructions reorder the bytes of DINT_1 according to a different order mode. The display style is ASCII, and each character represents one byte. Every instruction places the bytes, in the new order, in a different Destination.

Ladder Diagram

Example 2 - Swap the bytes in all elements of an array

Ladder Diagram

Example 3: SWPB on Structured Text

Structured Text

index := 0;

SIZE (array[0],0,array_length);

REPEAT

SWPB(array[index],REVERSE,array_bytes_reverse[index]);

index := index + 1;

UNTIL(index >= array_length)END_REPEAT;

Move/Logical Instructions

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