During ladder logic operation, what does the controller evaluate to determine each rung's status?

During ladder logic operation, what does the controller evaluate to determine each rung's status?

• A. The status of input and output tags.
• B. The status of internal timers alone.
• C. The status of input tags only, ignoring outputs.
• D. Random numbers.

Answer: (A)

In ladder logic, each rung is evaluated by checking the signals wired into that rung using the current values of input tags and any internal state that is referenced on that rung. That means you look at both the inputs and any output tags that are used as conditions (for example, a held or interlocked condition that involves the output). If all the required conditions on the rung are true, the rung is considered active and the coil on that rung will energize, updating the corresponding output tag. The outputs can feed back into logic, so their status matters for determining rung conditions, not because outputs drive the rung by themselves, but because they can be part of the logical path. Random numbers aren’t used, and internal timers influence the rung only insofar as their timing elements are part of the rung’s logic.

In ladder logic, each rung is evaluated by checking the signals wired into that rung using the current values of input tags and any internal state that is referenced on that rung. That means you look at both the inputs and any output tags that are used as conditions (for example, a held or interlocked condition that involves the output). If all the required conditions on the rung are true, the rung is considered active and the coil on that rung will energize, updating the corresponding output tag. The outputs can feed back into logic, so their status matters for determining rung conditions, not because outputs drive the rung by themselves, but because they can be part of the logical path. Random numbers aren’t used, and internal timers influence the rung only insofar as their timing elements are part of the rung’s logic.