RES — Reset

Clears the accumulator and status bits of a TIMER, COUNTER or CONTROL tag back to zero. The preset — .PRE or .LEN — is kept.

OperandsCopy Anchor Link

How It WorksCopy Anchor Link

Each structure has one field that counts up and one that says how far — and RES clears the first while keeping the second.

• Rung goes true → the counting field is cleared to 0 — .ACC on a TIMER or COUNTER, .POS on a CONTROL — and every status bit on the structure (.EN, .TT, .DN, .CU, .CD, .OV, .UN, .EU, .EM, .ER, .UL, .IN, .FD as applicable) is cleared to 0.
• The target is not touched: .PRE on a timer or counter, .LEN on a control.
• Rung goes false → RES does nothing.

RES is checked on every scan the rung is true, not just the rising edge. Holding the rung true holds the structure at zero.

Example — Clear a CounterCopy Anchor Link

Each rising edge on Button increments PartsCount.ACC. Pressing ResetCount clears the accumulator and PartsCount.DN.

When to UseCopy Anchor Link

• Clearing a retentive timer (RTO) — it is the only way to drop .ACC back to zero.
• Resetting a counter (CTU, CTD) — counters are retentive across rung transitions.

When Not to UseCopy Anchor Link

• A non-retentive timer (TON, TOF) already resets when its rung drops. Calling RES on it is redundant.

Common MistakesCopy Anchor Link

• Leaving the RES rung always-true — that holds the structure at zero forever and the timer or counter never runs.
• Restarting a timer on its own .DN to make it repeat (XIC(MyTimer.DN)RES(MyTimer)). The scan after RES only restarts the timer, so every cycle runs one scan longer than .PRE — two with XIO(MyTimer.DN) in front of the timer instead. That is fine for a flashing light, but a total counted from those cycles falls further behind every cycle. To keep time, let one timer run and work from its .ACC.

RelatedCopy Anchor Link

• Timers overview
• Counters overview
• RTO — retentive timer that requires RES
• CTU, CTD — retentive counters
• BSL and BSR — array instructions that keep their state in a CONTROL