Which timer instruction is used to begin timing when the rung goes true and hold the accumulated time when the rung logic goes false?

The timer instruction that begins timing when the rung goes true and holds the accumulated time when the rung logic goes false is the RTO (Retentive Timer On). This instruction allows the timer to accumulate time while the rung is true, and importantly, it retains the accumulated time even if the rung goes false. This means that if the condition becomes false, the timer does not reset to zero but instead holds the accumulated value, allowing it to continue timing from that point when the rung goes true again.

In contrast, other timers such as TON (Timer On Delay) start timing when the rung is true but reset to zero when the rung becomes false. The TOF (Timer Off Delay) starts timing only when the rung goes false, and the MCR (Master Control Reset) is used for controlling multiple rungs but does not specifically serve as a timer. Understanding the characteristics of these timers is crucial for effectively managing timing and control operations in programmable logic controllers (PLCs).