What are the common types of timers used in PLC programming?

Common PLC timer types: TON (Timer On Delay) - output energizes after input is true for preset time, used for startup delays. TOF (Timer Off Delay) - output stays on for preset time after input goes false, used for cooldown delays. RTO (Retentive Timer) - accumulates time and retains value when input goes false, requires reset instruction. TP (Pulse Timer) - generates fixed-duration pulse when triggered. Timers have current/accumulated value and done/enable status bits used in program logic.