Latch/Unlatch logic question: which statement best describes latch and unlatch behavior?

Latch/Unlatch logic question: which statement best describes latch and unlatch behavior?

• A. Latch forces instruction true even after de-energizing; Unlatch turns off the latch when rung is true
• B. Latch resets the instruction when rung is false; Unlatch holds the instruction true when rung is false
• C. Latch has no effect on the rung energization; Unlatch clears the Done Bit
• D. Latch affects only input states; Unlatch affects only output states

Answer: (A)

A latch introduces memory into a ladder rung. When the latch is set, the output stays true even after the input that set it goes false, because the latched state is stored. An unlatch acts as the reset: when its rung becomes true, it clears the stored state, turning the output off even if it was previously on. So, the combination described is that the latch keeps the instruction true after de-energizing, and the unlatch turns off that stored state when its rung is true. This matches how a set/reset (latch/unlatch) pair behaves in PLC logic.

A latch introduces memory into a ladder rung. When the latch is set, the output stays true even after the input that set it goes false, because the latched state is stored. An unlatch acts as the reset: when its rung becomes true, it clears the stored state, turning the output off even if it was previously on. So, the combination described is that the latch keeps the instruction true after de-energizing, and the unlatch turns off that stored state when its rung is true. This matches how a set/reset (latch/unlatch) pair behaves in PLC logic.