Data Movement & Bit ShiftingIntermediateIEC 61131-3

ROL (Rotate Left)

Rotates bits left; bits shifted out the left wrap around to the right.

The ROL (Rotate Left) function rotates the bits of the input value to the left by a specified number of positions. Unlike SHL, bits shifted out of the left end wrap around to the right end, so no data is lost. ROL is used for creating rotating bit patterns (sequencer outputs, LED chase patterns), implementing circular shift registers, and cyclic data manipulation.

Parameters

Inputs

Name	Type	Description
IN	ANY_BIT	Value to rotate
N	INT	Number of bit positions to rotate left

Outputs

Name	Type	Description
OUT	ANY_BIT	Rotated result

Ladder Logic Example

// Ladder Logic - ROL (Sequencer Pattern)
//
// |----[ Step_Pulse ]----[ROL]----|
// |                      IN: Pattern     |
// |                      N:  1           |
// |                      OUT: Pattern    |

Structured Text Example

// Rotating LED chase pattern
IF Step_Pulse THEN
    LED_Pattern := ROL(LED_Pattern, 1);
END_IF;
// 0000_0001 -> 0000_0010 -> 0000_0100 -> ... -> 1000_0000 -> 0000_0001

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Platform-Specific Implementation

Siemens (TIA Portal)

Use ROL instruction in TIA Portal.

Allen-Bradley (Studio 5000)

No native ROL; implement using BSL with feedback from last bit.

CODESYS

Use ROL() function in ST.

Common Applications

LED chase/sequencer patterns
Circular shift registers
Rotating bit patterns for outputs
Cyclic data manipulation
Round-robin scheduling

Frequently Asked Questions

What is ROL (Rotate Left) in PLC programming?

Rotates bits left; bits shifted out the left wrap around to the right. The ROL (Rotate Left) function rotates the bits of the input value to the left by a specified number of positions. Unlike SHL, bits shifted out of the left end wrap around to the right end, so no data is lost.

What are common applications of ROL (Rotate Left)?

ROL (Rotate Left) is commonly used for: LED chase/sequencer patterns, Circular shift registers, Rotating bit patterns for outputs, Cyclic data manipulation, Round-robin scheduling.

How do I use ROL (Rotate Left) in different PLC platforms?

Siemens: Use ROL instruction in TIA Portal. Allen-Bradley: No native ROL; implement using BSL with feedback from last bit. CODESYS: Use ROL() function in ST.