The RevPi DIO connection identified as Option A gives direct, active-high behavior: apply 24 V to Digital Input 1 for HIGH, and wire DO through the light to GND so the light turns on when the output goes HIGH. Confirm the exact connector and terminal assignments in the module datasheet before applying power.
Reject the quick fixes first
Do not start by moving wires until the light reacts. That can produce an apparently working circuit with inverted logic, or place 24 V on the wrong connector position when terminal numbering is unclear.
| Quick fix | What happens | Required action |
|---|---|---|
Connect Digital Input 1 directly to GND |
The input remains at the low reference and does not register the intended state change. | Switch the input to 24 V for the active state. |
Connect the light between 24 V and DO
|
The light can turn on when DO goes LOW, reversing the expected command. |
For active-high operation, connect DO to the light and the other side of the light to GND. |
| Guess connector positions from a sketch | The electrical idea may be correct while the physical terminal is wrong. | Match every wire to the connector view and terminal description in the exact module datasheet. |
| Test with an unverified load | A functional test can exceed an unstated output or load rating. | Read the output rating and load current from their datasheets before energizing. |
Get it running, then fix it properly: a temporary diagnostic connection still needs identified terminals, compatible ratings, and a documented final schematic.
Measure the input branch
Start with the input because its two expected states are simple. Measure voltage from the Digital Input 1 signal conductor to the circuit GND while commanding the input off and on.
- With the command off, confirm that the signal is at the low reference.
- With the command on, confirm that the signal changes to 24 V.
- Observe the input state in the controller or diagnostic interface. The 24 V condition must register HIGH.
- If the voltage never leaves GND, trace the switch or jumper path. A direct connection to GND cannot generate the required HIGH transition.
- If 24 V reaches the physical input but the displayed state does not change, verify that the wire is on the terminal assigned to
Digital Input 1and that the software is reading the matching channel.
A digital input detects a voltage relative to its reference. Holding the signal at GND keeps it below the active threshold; changing software labels or reversing display colors does not create an electrical transition. The exact threshold is module-specific, so read it from the datasheet when a measured input voltage is neither clearly 0 V nor 24 V.
Determine the output logic
Next, command DO LOW and HIGH while observing the light. Use the branch below to separate a wiring problem from an inverted command.
| Observed behavior | Meaning | Next check |
|---|---|---|
| Light is off at LOW and on at HIGH | The output is operating with the intended active-high logic. | Proceed to connector and rating checks. |
| Light is on at LOW and off at HIGH | The load is connected in the Option B arrangement between 24 V and DO. |
Move the load to the active-high arrangement, or deliberately account for inverted logic if the design requires it. |
| Light never turns on | The load lacks a complete path, the command is not reaching the channel, or the load/output is incompatible. | Verify the command state, both load wires, connector position, and published ratings. |
| Light never turns off | The load may be bypassing the controlled path, or the selected channel is not the one being commanded. | De-energize and trace the circuit against the connector view. |
Option B is not the normal choice for direct command-to-state behavior. Its light can operate, but LOW becomes the energizing command. That inversion creates recurring maintenance faults because an HMI indication, PLC command, and field device no longer share the same meaning.
Confirm the connector before energizing
The wiring concept does not identify physical connector positions. Open the datasheet for the exact RevPi DIO module and record the connector designation, terminal number, channel function, 24 V connection, GND connection, and output rating on the schematic.
- Match the module name on the hardware to the datasheet title.
- Use the connector orientation marker from the datasheet; do not infer numbering from cable-entry direction.
- Continuity-check each unpowered field wire from the connector to the switch or light.
- Compare the light current and supply requirements with the published output limits.
- Stop if the connector orientation, terminal numbering, output type, or rating remains unclear. Do not use power application as a terminal-identification method.
Wire the active-high arrangement
After identifying the terminals and checking ratings, build Option A.
- De-energize the field circuit and verify that voltage is absent at the conductors being moved.
- Wire the input so its active condition applies 24 V to
Digital Input 1. Its inactive condition must remove that active voltage rather than hold the input permanently active. - Wire
DOto one side of the light. - Wire the other side of the light to GND.
- Check that no strand or jumper shorts 24 V directly to GND or bypasses the light.
- Restore power only after the field wiring matches the verified connector data.
Do not insert software inversion to disguise Option B during commissioning unless active-low operation is a deliberate, documented design decision. Software inversion may make the screen look correct while leaving the field circuit opposite to the next technician’s expectation.
Verify both states and record the result
- Command the input inactive and confirm that the controller reports LOW.
- Apply 24 V to
Digital Input 1through the intended field device and confirm HIGH. - Command
DOLOW and confirm that the light is off. - Command
DOHIGH and confirm that the light is on. - Repeat the complete cycle several times while watching for delayed, intermittent, or inverted indications.
- Update the schematic with the verified connector positions, channel names, active-state voltage, and load connection.
If the field voltage changes correctly but the software state does not, investigate channel mapping or module diagnostics. If the software command changes correctly but the load does not, stay on the output branch: check the physical channel, wiring continuity, supply reference, load compatibility, and output diagnostics.
FAQ
Why does my RevPi DIO input stay LOW?
A connection from Digital Input 1 directly to GND holds the signal at the low reference. Apply 24 V for the active condition, then confirm that the controller reports HIGH.
Why does the RevPi DIO light turn on when DO is LOW?
The light is wired in the Option B arrangement between 24 V and DO, which produces inverted operation. For active-high behavior, wire DO to the light and the other side of the light to GND.
Why does changing the PLC logic not fix the DIO wiring?
Software inversion can hide the symptom but leaves the electrical behavior active-low. Correct the wiring to Option A unless inverted operation is an intentional, documented requirement.
When should I stop troubleshooting RevPi DIO wiring?
Stop if connector orientation, terminal numbering, output type, ratings, or diagnostic status cannot be confirmed from the exact module datasheet. Leave the circuit de-energized and escalate to official Revolution Pi support with the module identification, schematic, voltage readings, commanded states, and observed results.