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S5 AWL Command: S (Set)

S5 AWL instruction S (Set): Sets a bit to TRUE when VKE is TRUE. The bit stays TRUE until explicitly reset with R.

·2 min read
S5AWLSSetSetzenlatchflip-flopbit logic

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S5 AWL Command: S (Set)

The S instruction sets a boolean operand to TRUE when the VKE is TRUE. Unlike the = (assign) instruction, S is a latching operation — the bit stays TRUE even when the VKE becomes FALSE. It can only be turned off with the R (Reset) instruction.

Syntax

S  <operand>

S7 Equivalent

S5 AWLS7 STLS7 SCL
S A 4.0S Q 4.0 (EN) / S A 4.0 (DE)Set via SR/RS flip-flop or IF condition THEN output := TRUE; END_IF;

Code Example — Set/Reset Pair

U  E 0.0       // Start button (momentary)
S  A 4.0       // Set motor ON → stays ON

U  E 0.1       // Stop button (momentary)
R  A 4.0       // Reset motor OFF

Behavior: Pressing Start sets the motor. It stays on. Pressing Stop resets it. This is the classic Set/Reset (SR) flip-flop pattern.

Priority rule: If both S and R are TRUE in the same cycle, the last operation wins. In the example above, R comes after S, so Reset has priority. Swap the order to give Set priority.

Common Errors

Using S without a matching R: The bit stays TRUE forever. Always ensure every S has a corresponding R somewhere in the program.

Related Commands

Part of the S5 AWL Command Reference. Maintained by PLCcheck.ai.

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