ComponentPorts

Component Ports

Table of contents

• Introduction
• Background
• Details

Introduction

In PLM projects it is possible to implement Inports and Outports for programs. Additionally member variables of the component can be declared as ports. This declaration is basically explained in the components header file created by PLCnCLI. Since the life-time of a component differs from the programs life-time, some additional implementation is necessary if the component ports shall be initialized similar to program ports regarding to the Cold/Warm Start behavior of the PLC application! This example demonstrates the necessary implementation.

Background

The PLCnext firmware creates program instances according to the ESM configuration when the PLC program is loaded. Program instances are deleted when the PLC application is unloaded. This holds true for component instances as well. Additionally (and in contrast to component instances) program instances are also deleted and created again when the PLC application is started (Cold as well as Warm Start). During this creation all member variables of the program are initialized by the C++ code. If the PLC is started by a warm start, program ports which are marked with the Retain attribute are restored to their last saved value. This is handled for program instances by the firmware but for component instances dedicated C++ code has to be provided within the component.

This dedicated C++ code consists basically of one method added to the component. This method has to be registered at the firmware to be called when the PLC application is started. The input parameter of this method then indicates the start kind (warm/cold) of the PLC application.

Details

Precondition: The header files Arp/Plc/Commons/Domain/PlcStartKind.hpp and Arp/Plc/Commons/Domain/PlcDomainProxy.hpp need to be included as well as the namespace Arp::Plc::Commons::Domain needs to be used.

The ComponentWithPort in this example declares the ports retainPort1 and nonretainPort1 and the first port is marked with the Retain attribute. Furthermore the method OnPlcStarting(PlcStartKind) is defined. The component registers this method to the firmware PlcDomainProxy within its Initialize() method. It is important to unregister this method when the components life-time ends. This is done within the Dispose() method. Please note that this method may not be declared automatically when PLCnCLI creates a new component.

Within the OnPlcStarting(PlcStartKind) method the input startkind is checked:

• The value Warm indicates a Warm Start of the PLC application. Such Warm Start can be performed using PLCnext Engineer or after the PLC has booted.
• The value RestoreWarm indicates a Warm Start of the PLC application in the context of the PLCnext Engineer function "Restore last saved retain data".
• The value Cold indicates a Cold Start of the PLC application which can be performed using PLCnext Engineer.
• The value Hot indicates a Hot Start of the PLC application which can be performed using PLCnext Engineer. In this case all ports are expected to keep their values, so no action is required.

Note: The program in this example is created by PLCnCLI and has not been changed. In PLCnext Engineer this program needs to be instantiated in order to create an instance of ComponentWithPorts.