Devices AccessTypes Reference

Control how data is read and written.

Reference → Modules → Devices → UI → Points | Protocols | Channels | Nodes | AccessTypes | Monitor

Creating AccessTypes

1. Navigate to Devices → AccessTypes
2. Click Plus icon
3. Configure properties
4. Click OK

AccessType Properties

Read Configuration

Write Configuration

Advanced Settings

Common AccessType Patterns

Continuous Monitoring

Name: AlwaysRead
ReadPolling: Always
ReadPollingRate: 1000
WriteEvents: False
OnStartup: True

Control Points

Name: ReadWrite
ReadPolling: Always
ReadPollingRate: 500
WriteEvents: True
WriteEvent: OnChange

Event-Driven

Name: Triggered
ReadPolling: Never
ReadTrigger: @Tag.ReadNow
WriteEvents: True
WriteTrigger: @Tag.WriteNow

OnDisplayOrServer Mode

Optimizes communication by activating points only when needed.

How It Works

OnDisplay Behavior:

• Points activate when display opens
• Deactivate when display closes
• Reduces unnecessary communication
• Improves system performance

OnServer Behavior:

• Always active when OPC Server running
• Required for server-side logic
• Scripts, alarms, expressions need this

Configuration

1. Set ReadPolling to OnDisplayOrServer
2. Configure ReadPollingRate
3. Enable WriteEvents if needed
4. Assign to relevant points

Use Cases

Display-Driven:

Line A Display → Line A Tags Active
Line B Display → Line B Tags Active
No Display → No Communication

Server Requirements:

• Script Tasks
• Class Methods
• Expressions
• Alarm Conditions

<ac:structured-macro ac:name="info"> ac:rich-text-body Server-side tags (used in scripts, alarms, expressions) require an AccessType with ReadPolling set to "Always" or a separate AccessType for OnDisplayOrServer mode. </ac:rich-text-body> </ac:structured-macro>

Trigger-Based Operations

Read Triggers

csharp

// Trigger read when button pressed
ReadTrigger: @Tag.RefreshButton

// Periodic trigger
ReadTrigger: @Tag.Timer.SecondTick

// Conditional trigger
ReadTrigger: @Tag.ProductionActive && @Tag.ShiftRunning

Write Triggers

csharp

// Write on command
WriteTrigger: @Tag.SendCommand

// Batch write
WriteTrigger: @Tag.BatchReady

// Conditional write
WriteTrigger: @Tag.Value > 100

Performance Optimization

Polling Rate Guidelines

Block Commands

For protocols supporting block transfers:

UseStaticBlocks: True
BlockCommand: "READ_BLOCK:100:50"

Benefits:

• Reduced overhead
• Faster updates
• Lower network traffic
• Improved efficiency

Check driver documentation for supported commands.

Best Practices Checklist

• Group Similar Points - Same polling requirements
• Use OnDisplayOrServer - For HMI-only data
• Minimize Always Polling - Only critical points
• Set Appropriate Rates - Match process dynamics
• Use Triggers Wisely - Reduce continuous polling
• Configure Startup Reads - Initialize important values
• Test Performance - Monitor CPU and network load

Troubleshooting

Points not updating:

• Verify ReadPolling enabled
• Check polling rate
• Confirm display open (OnDisplay)
• Review trigger conditions

Write failures:

• Confirm WriteEvents enabled
• Check WriteEvent setting
• Verify trigger firing
• Review point access rights

Performance issues:

• Reduce polling rates
• Use OnDisplayOrServer
• Implement triggers
• Enable block commands

OnDisplay not working:

• Verify display contains tags
• Check AccessType assignment
• Confirm display runtime active
• Review server-side usage

Examples by Industry

Manufacturing

HMI Points: OnDisplayOrServer, 500ms
Alarms: Always, 250ms
Reports: Triggered, OnDemand

Building Automation

HVAC: Always, 5000ms
Lighting: OnDisplayOrServer, 1000ms
Energy: Always, 60000ms

Process Control

Critical: Always, 100ms
Process: Always, 1000ms
Historical: Triggered, 5000ms