HOAKKK (Customer) asked a question.
I watched this video tutorial and saw that using C0 to store when stopping and running still retains the value before stopping
https://www.youtube.com/watch?v=B0yAS4XJItg&ab_channel=ACCAutomation
But when I write the program, C0 does not save the value when running
Stop
When running again, C0 does not hold the value when turned on
Stop Losing Your PLC Outputs After a Power Failure! 🛑
Learn PLC memory retention in Do-More Designer — route outputs through a retentive bit so their last state survives a power failure and recovers on restart.
⚡ QUICK ANSWER
By default a PLC output drops to off on power loss; memory retention keeps its last state through a power cycle. In Do-More Designer you route the logic to a retentive memory bit (like C0) instead of firing the physical output directly, then add a rung where that retentive bit drives the real-world output (Y0). When power fails and returns, C0 restores its last state and the output comes back exactly as it was. Which memory locations are retentive varies by controller, so check the documentation. The full step-by-step is in the written guide below.
📖 FULL STEP-BY-STEP + DOWNLOADS (free beginner series & simulator)
https://accautomation.ca/programming/plc-beginners-guide/
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https://www.youtube.com/playlist?list=PL3y71jAPOdZB5LJMMotZP36LvzfdgkgzW
⏱️ TIMESTAMPS
0:00 - Introduction: Memory Retention
0:18 - Testing the Current Program (Seal-In)
0:30 - What Retentive Memory Does on Power Loss
0:51 - Entering Edit Mode
1:01 - Changing the Output to a Retentive Bit (C0)
1:48 - Checking the Controller Documentation
2:04 - Inserting a Rung for the Real Output (Y0)
2:44 - Saving & Writing to the PLC
2:54 - Testing Memory Retention
3:11 - Power Cycle Test Results
3:25 - Best Practices & Wrap Up
📚 WHAT YOU'LL LEARN
✅ Why a standard PLC output loses its state on power loss
✅ Route logic to a retentive memory bit (C0) instead of firing the output directly
✅ Add a rung so the retentive bit drives the real-world output (Y0)
✅ Check the controller documentation for which memory is retentive
✅ Power-cycle test to confirm the output returns to its last state
❓ FREQUENTLY ASKED
Q: How do you make a PLC output retentive in Do-More Designer?
A: Route the logic to a retentive memory bit (like C0) rather than the physical output, then add a rung where that bit drives the real output — so the state survives a power cycle. Full steps are in the guide.
Q: Which memory locations are retentive on a PLC?
A: It varies by controller, so check your model's documentation — some ranges are retentive by default and others aren't. The video shows where to look.
Q: What happens to a non-retentive output after a power failure?
A: It returns to off when power comes back, regardless of its state before the failure — which is why critical outputs should be routed through retentive memory.
👉 Full step-by-step & downloads: https://accautomation.ca/programming/plc-beginners-guide/
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Regards,
Garry
ACC Automation
http://www.accautomation.ca
https://www.youtube.com/watch?v=B0yAS4XJItg&ab_channel=ACCAutomation
The behavior you are describing is not related to rententive memory. By default, C0 through C2047 are set to RETENTIVE (this can be observed and modified in PLC > System Configuration > Memory Configuration). If you were to set element C1 to TRUE in a Data View while the Simulator were RUN mode and then transition from RUN to STOP to RUN again, you would see that C1 is still TRUE.
The behavior you are seeing with C0 in your logic is related to Termination Scan Behavior. One of the many actions that will take place when a Program code-block terminates is ALL of the Output Coil (OUT) instructions will be turned OFF. See Help Topic DMD0232 in the Do-More Designer software help file for a brief overview of Termination Scan Behavior. For more information on Termination Behavior, see Help Topic DMD0192.