mobileFX WebKitX CEF3 ActiveX 4.x
WebKitXCEF3Lib ActiveX Control / Settings Object / hmi_input_clock_frequency_hz Property
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hmi_input_clock_frequency_hz Property
In This Topic
Description

HMI input signals latch frequency in Hz.

Property type
Read-write property
Syntax
Visual Basic
Public Property hmi_input_clock_frequency_hz As Double
Remarks

With WebKitX you can create HMI Dash Boards by forwarding sensor data to HTML and JavaScript for rendering. The input signals are latched and the clock frequency is controlled by Settings.hmi_input_clock_frequency_hz which defaults to 2Hz. This means that input signal values are buffered by WebKitX and are flushed to HTML/JavaScript every 500 milliseconds. If no input signals are registered since last flush then no emission takes place. You can disable the input latch and pass the input signal values at real-time by setting the Settings.hmi_enable_input_clock to False.

It is important to understand that input signals travel over Interprocess Communication (IPC) from the ActiveX to Chromium Engine which are the processed by JavaScript and eventually alter the DOM of the HTML HMI user interface. This is a time-consuming process and therefore you must limit the hmi_input_clock_frequency between 0.1 Hz and 60 Hz. The upper limit of 60 Hz is equivalent to screen refresh rate of 60 fps (frames per second) or screen refresh every 16.7 milliseconds. Even though Chromium supports 60 fps rendering for Hardware Accelerated Graphics (WebGL), you should not push beyond 60 Hz. 

Example
Option Explicit

Private Sub Form_Resize()
    On Error Resume Next
    WebKitX1.Move 0, 0, ScaleWidth, ScaleHeight
    Err.Clear
End Sub

Private Sub Form_Load()
    
    ' Load Human Machine Interface markup
    WebKitX1.HMI_URL = "file:///" + App.Path + "/index.html"
    
End Sub

Private Sub WebKitX1_OnCreate(ByVal Settings As WebKitXCEF3Lib.ISettings, CommandLineSwitches As String)
            
    ' Set WebKitX HMI values to flush/refresh at rate 1Hz (every 1sec).
    Settings.hmi_enable_input_clock = True
    Settings.hmi_input_clock_frequency_hz = 1
    
End Sub

Private Sub WebKitX1_OnPageComplete(ByVal url As String)
               
    ' We use a timer at 60Hz to simulate high-frequency sensors.
    Timer1.Interval = (1000 / 60)
    Timer1.Enabled = True
    
End Sub

Private Sub Timer1_Timer()
    
    ' We read values from "sensors" and pass them to six (6) different HMI I/O channels.
    ' We read sensor values 60 times per second (every ~16ms). WebKitX uses input latches
    ' to retain input values and flush them to HTML at a rate of 1Hz (every 1sec).
    
    WebKitX1.HMI_VALUE_001 = Rnd * 1560
    WebKitX1.HMI_VALUE_002 = Rnd * 1560
    WebKitX1.HMI_VALUE_003 = Rnd * 1560
    WebKitX1.HMI_VALUE_004 = Rnd * 1560
    WebKitX1.HMI_VALUE_005 = Rnd * 1560
    WebKitX1.HMI_VALUE_006 = Rnd * 1560
            
End Sub

Private Sub WebKitX1_OnHMIControlSignal(ByVal Index As Long, ByVal Data As String)

    Debug.Print Format(Time, "HH:MM:SS") & " > HMI_VALUE_" & Format(Index, "000") & " = " & Data

End Sub
See Also

Settings Object  | Settings Members  | HMI_VALUE_001 Property

Guides

Getting Started with Rockwell FactoryTalk

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