Which pair of coil operations are used to implement memory in ladder logic?

• A. Set & Hold and Reset Coil
• B. Non-Latching Coil and Inverse Non-Latching Coil
• C. Coil operations of a ladder diagram
• D. Memorized ON and Memorized OFF

Answer: (A)

Memory in ladder logic is created with a latch that can remember a state. The Set operation turns the memory on and, through its holding (seal-in) contact, keeps the rung energized even after the triggering input goes away. The Reset operation clears that memory, turning it off when commanded. Together, Set with a hold path and a Reset coil form an SR latch inside the ladder diagram, which is exactly how the program remembers a condition until it’s changed. Other options don’t provide a lasting state: non-latching coils only energize while their input is true and don’t hold memory; the inverse non-latching coil behaves similarly with inverted logic; a generic description of coil operations or nonstandard terms like memorized ON/OFF aren’t actual memory elements in ladder logic.