Runnable simulator field guide
PLC latch and start scenario: test checklist
Direct answer
The learner can explain who owns maintained state, prove stop priority and test held, simultaneous, reset and power-return conditions.
Written for pLC beginners learning seal-in branches or set-reset state and the conditions required for deliberate stopping and restart.
Scenario setup
Start request, stop condition, maintained-state owner, seal contact or set-reset pair, permissives, feedback, reset authority and restart policy.
I/O and state map
Momentary command through rung or state instruction, maintained bit, final output, physical response, independent feedback and deliberate stop path.
Normal run
Start pulse establishes the required state, release preserves it and stop reliably removes it over repeated cycles.
Boundary run
Start and stop together, held start, held reset, lost permissive, failed feedback, duplicate writer, download and power return.
Injected fault
A command, priority, branch, state-owner, reset, retentive, output, feedback or restart mismatch.
Target check
The chosen pattern tested on the exact target controller with physical interlocks and machine acceptance cases.
What is a latch in PLC programming?
It is maintained state that remains after the initiating condition changes until a defined reset or stop path clears it.
Should start or stop have priority?
Most start-stop contracts give stop priority, but the required simultaneous-input behavior must be written and tested for the machine.