Wonderware InTouch Left Key Down Script: Permissive Logic

When building a motor start permissive on an HMI, AVEVA (formerly Wonderware) InTouch provides several mouse and keystroke event triggers. The On Left Key Down and While Left Key Down actions fire on button press, while On Left Click fires on release. For interlock checks such as pressure must be less than or equal to 10 and fault count must equal zero before the operator can start the motor, QuickScript is wired to the button's action property. This reference covers the script syntax, event trigger selection, Modbus tag configuration, and the architectural decision of whether to place permissive logic in the PLC or the HMI.

1. Overview of the Permissive Pattern

A motor start permissive is a guard condition that must evaluate true before the HMI releases the start command downstream to the controller. The most common permissive fields are:

• Process variable confirmation (pressure, temperature, level, flow)
• Fault aggregation (no active faults, drive ready bit, E-stop clear)
• Mode selection (Remote/Local, Auto/Manual, In Remote)
• Operator authentication (key-switch, user level, two-step confirm)

When the source data arrives over Modbus/TCP into InTouch IO tags, the HMI becomes the natural place to evaluate the permissive because the PLC tag may not be writable from the operator console. When the data is backplane-routed from a ControlLogix, CompactLogix, or PLC tag server, the permissive is best evaluated in the PLC and surfaced to the HMI as a single permissive_ok tag.

2. Prerequisites

3. Event Trigger Comparison: On Left Click vs On Left Key Down vs While Left Key Down

AVEVA InTouch exposes three mouse event triggers on button objects. Choosing the wrong trigger changes when the permissive fires and how often the script re-evaluates while the operator holds the button.

According to AVEVA's While Left Key Down / While Key Down reference, the periodic trigger accepts a Frequency parameter expressed in milliseconds with a valid range of 1 to 360000. A typical value for a permissive re-check is 100-500 ms. AVEVA's Configure an action script animation with a mouse-down event guide also clarifies that mouse-down events trigger two separate signals, and the script should be idempotent to handle both safely.

4. Configuring the Button in WindowMaker

1. Open WindowMaker and load the window containing the motor faceplate.
2. Double-click the Start button to open the Button Properties dialog.
3. Switch to the Action tab (or Touch Links / Animations on older builds).
4. In the Mouse or Touch/Click section, click the cell next to On Left Key Down (or While Left Key Down for a held check).
5. Select QuickScript as the action type and click Edit.
6. Paste the permissive script (see Section 5) and click OK.
7. Save the window. Run WindowViewer to test.

5. QuickScript Syntax for the Permissive

The original control logic the operator wants is:

If pressure <= 10 AND faults = 0 THEN start = 4

In InTouch QuickScript, the equality comparison is == (double equals), the assignment operator is = (single equals), and logical conjunction is the keyword and. The corrected syntax is:

If pressure <= 10 and faults == 0 then
    start = 4;
EndIf;

The trailing semicolon is optional but recommended. The EndIf keyword terminates the block. Whitespace and case (If/if) are flexible, but AVEVA's editor will normalise casing on save.

5.1 Writing to a Modbus Coil or Holding Register

If start is an IO tag pointing at a Modbus holding register, the assignment start = 4; writes the value 4 to that register. To start a motor, a more idiomatic write is to a discrete coil (0 or 1):

If pressure <= 10 and faults == 0 and not motor_running then
    start_cmd = 1;
EndIf;

For a one-shot pulse (rising edge, auto-reset), use the InTouch ! operator or a memory discrete tag:

If pressure <= 10 and faults == 0 then
    start_pulse = 1;
EndIf;

Reset the pulse on the next scan or after a Wait timer.

5.2 Adding Operator Feedback (Disable Animation)

To make the button visibly disabled when the permissive fails, wire a Disable animation on the same button object:

1. Select the button, choose Animation Links > Disable.
2. Set the expression to pressure > 10 or faults != 0.
3. Enable the Disable color override (typically gray fill).

The button is now grayed out when the permissive fails, providing a visual cue that the operator should not press it.

5.3 Full Example with Logging

{ This script runs on On Left Key Down of the Start button }
If pressure <= 10 and faults == 0 then
    start_cmd = 1;
    last_start_reason = "OK";
Else
    If pressure > 10 then
        last_start_reason = "BLOCKED: High Pressure";
    EndIf;
    If faults != 0 then
        last_start_reason = "BLOCKED: Active Faults";
    EndIf;
EndIf;

6. Reading Modbus Data into InTouch

When the source data is a Modbus slave (PLC or remote RTU), configure an Access Name in the InTouch Access Names dialog:

The IO tag definitions then reference the Access Name and the Modbus address:

The DAServer (such as DASMBTCP for Modbus/TCP or DASMBRTU for Modbus/RTU) polls the device at the configured rate and publishes updates to InTouch via SuiteLink. Writes from QuickScript propagate back to the slave through the same channel.

7. PLC vs HMI Permissive Logic

The trade-off between placing interlock logic in the PLC and evaluating it in the HMI is one of the recurring questions in supervisory control design.

Recommendation: Place safety-critical and process-critical interlocks in the PLC. Reserve HMI permissives for operator ergonomics - hiding the start button when not in remote, disabling the button when a known fault is active, or requiring a two-step confirm for high-energy equipment. For SIL-rated functions, follow IEC 61511 and keep the safety loop in the safety PLC; do not rely on the supervisory HMI for safety.

8. Verification and Testing

1. Tag Watcher. Open the DbDump or Tag Viewer in WindowViewer. Verify pressure, faults, and start_cmd are updating at the expected scan rate.
2. Permissive positive path. Force pressure = 8.0 and faults = 0 in the Watcher. Click the Start button. Confirm the value 4 is written to the start tag and the slave device receives the write.
3. Permissive negative path. Force pressure = 12.0. The script's If condition is false; no write should occur. Confirm via the Watcher and the slave's diagnostic page.
4. Animation verification. The button should be enabled (normal color) when the permissive is true and disabled (gray) when the permissive is false. Toggle faults between 0 and 1 to confirm the visual state flips.
5. Event log. If the script writes to last_start_reason, view the value in the Watcher to confirm the correct branch is being taken.
6. Network loss test. Disconnect the PLC network cable. The InTouch tag should mark $AccessFault for the Access Name; the button should be disabled and the script should not fire on click.

9. Troubleshooting Matrix

10. Operational and Migration Notes

• Avoid placing permissives on the HMI in SIL 2 / SIL 3 paths. Use a safety PLC and a dedicated safety I/O loop for those functions.
• Use QuickScript > Conditional scripts for one-time events, Data Change scripts for state-transition triggers, and Active window scripts for window-level behavior.
• When migrating from InTouch 2014 to 2020 R2 or later, scripts that use EQ, NE, GT, LT may need rewriting to ==, !=, >, <. The legacy operators are deprecated but still parse.
• Keep the script body short. Long QuickScripts on On Left Key Down can stall the WindowViewer redraw thread on slow panels.
• Always pair the permissive write with an InTouch alarm that fires when the script blocks the action. This gives the operator a log entry that explains why the start command was suppressed.

11. Frequently Asked Questions