Wake an HMI screen from screen saver on a PLC schedule

What you need

• The panel project software and its manual. One panel family keeps the sleep trigger in the project attributes under a tab called "PLC to Panel", as an item named Trigger Screen Saver (Discrete); turning that bit on puts the touch screen into screen saver mode. Your manual names its equivalent.
• The screen-change mechanism for the same project, and the number or name of the startup screen operators should see at 6:00 AM.
• A PLC with a real-time clock, and the time-of-day scheduling method you already trust on that controller.
• An agreement with operators about alarms at night, because a displayed alarm wakes the panel before 6:00 AM.

Put the panel to sleep at 5:00 PM

1. Find the screen saver trigger in the project and write down the PLC address it maps to. The mapping belongs to the project, so read the address from the project editor or the manual instead of guessing it.
2. Note whether the trigger acts on the bit's state or on its change. One panel family loads the screen saver on both edges, when the value changes from 0 to 1 and again from 1 to 0. If the manual does not say, the bench test in the checking section settles it.
3. In the PLC, compare the clock against 17:00 and command the mapped bit from that comparison through a one-shot. A comparison on hours and minutes stays true for 60 seconds, so without the one-shot the bit re-commands on every scan for a full minute.
4. Leave the inactivity timer alone. It sleeps the panel after idle minutes during the day; the PLC bit owns the fixed 5:00 PM bedtime.

The schedule compares against the PLC clock, so keep that clock matched to the time your shifts run on. When daylight saving time moves the local hour, update the clock or the 5:00 PM command fires at 6:00 PM wall time. Setting a PLC clock from the operator panel for daylight saving time walks through the clock write.

Wake the panel at 6:00 AM with a screen change

1. Build the wake as a screen change. Changing the displayed screen wakes a panel in screen saver mode, and it needs no operator present.
2. At 06:00, issue a one-time screen change to the startup screen, through a one-shot again, so the command fires once and does not hold operators on the startup screen for the rest of the shift. The write itself, and giving control back to the operator afterward, are covered in changing an HMI screen from the PLC and giving control back.
3. Match the bit handling to your trigger kind. If the panel wakes when the bit clears, the trigger is state-acting: hold the bit from 5:00 PM and clear it as the 6:00 AM screen change lands. If the panel stays asleep after the bit clears, pulse the bit for one scan at bedtime and leave it clear, so no edge remains to put the panel back to sleep in the morning.
4. If the manual lists a wake trigger as well, use it in place of the screen change: one family's version raises the screen brightness to the level held in a linked register, and the panel clears that bit once it has acted.

Keep touch wake working, and plan what alarms do

Leave the panel's touch behavior untouched. One touch should bring the display back with the panel asleep, exactly as it does now; test that first, because it is the behavior operators rely on at 2:00 AM. Then ask one question: does the touch that wakes the display also reach the project underneath? Users on at least one panel family ask for a screen saver that swallows the waking touch. If your panel passes the first touch through to the screen, keep a confirmation step on any control that starts the machine.

Alarms behave as configured: an alarm set to display wakes the panel, and the alarm's display option has to be enabled for it to show at all. On a night with an alarm, the screen is lit before 6:00 AM, which is usually what operators want, since the alarm is the reason to walk over. Agree on it in advance so a lit screen at night reads as an alarm, not as a fault in the schedule. Waking on a machine fault is a common variant of this, and a knowledge base page on waking a screen saver on a machine fault shows one panel's alarm-trigger setup.

How to check it worked

1. Bench test the trigger kind. Command the mapped bit on, leave it on for one minute, then clear it while watching the panel. A panel that wakes when the bit clears takes the held-bit variant; a panel that stays asleep takes the bedtime pulse.
2. Test the schedule without waiting for the shift to end. Set the PLC clock to 4:59 PM, wait 60 seconds, and confirm the bit commands once and the panel sleeps.
3. Test touch. With the panel asleep, touch once and confirm the display returns.
4. Test the alarm path. Force a test alarm with its display action enabled while the panel is asleep, and confirm the screen lights.
5. Test the morning wake. With the panel asleep, command the screen change at a test time and confirm it lands on the startup screen; then navigate away and confirm nothing drags the panel back. If your panel switches screens through a register, a value that never changes can be ignored as no change, and retriggering the same screen value on a PLC-to-panel screen switch register shows the fix.
6. If the panel stayed awake during testing, look at the link. On a polled serial link, a dropped bit write leaves the panel lit, and why PLC-triggered messages drop on a serial HMI panel covers making those writes arrive.

Example: sleep at 5:00 PM, wake at 6:00 AM

Inputs, each with its source:

• Bedtime 17:00 (5:00 PM) and wake 06:00 (6:00 AM), the overnight window this setup targets.
• The screen saver trigger bit, at the address your project's PLC-to-panel mapping assigns.
• Clock comparison resolution of 1 minute, so each command window lasts 60 seconds.
• Trigger kind, change-acting or state-acting, settled by the one-minute bench test.

Rule in words: command the sleep trigger once at bedtime, wake the panel with a one-time screen change at wake time, and let touch and displayed alarms work as they normally do.

Arithmetic: the dark window runs from 17:00 to 06:00, which is 7 h to midnight plus 6 h more to 06:00, or 13 h 0 min. Each clock comparison is true for 60 seconds; the one-shot takes the first scan of the window, so the trigger commands once at 17:00 and the screen change fires once at 06:00.

Result: on a change-acting trigger, the bit pulses at 17:00 and the panel sleeps for 13 h 0 min unless an operator touches it or an alarm displays. On a state-acting trigger, the PLC holds the bit for the full 13 h 0 min and clears it as the 06:00 screen change lands.

Decision: pulse at bedtime for a change-acting trigger, hold the bit for 13 h for a state-acting trigger, and build the wake as the 06:00 screen change either way. The bench test picks the variant in one minute.

When this setup is the right one

Recommendation: Keep the inactivity timer for daytime idle sleep, add the 5:00 PM command on the mapped screen saver trigger, and wake the panel at 6:00 AM with a one-time screen change to the startup screen. Pulse the bit at bedtime unless the bench test shows the panel waking when the bit clears; in that case hold it until the morning change. A panel with no mappable trigger still takes half the schedule: let it fall asleep on its inactivity timer after the last touch of the day and keep the 6:00 AM screen change as the wake. If operators want the screen lit through the working day even when idle, shorten or switch off the inactivity timer in the project settings and let the PLC bit own the only fixed bedtime.

Questions