System Manager and PLC Manager 

System Manager

PLCnext Technology is by definition an open platform. This means that as a user you can integrate your own components and programs. During firmware startup, the System Manager ensures that all integrated components and programs are configured and started in the correct order. Here, all system processes are generated and function extensions are supplemented. A system component is always started, configured and shut down by the System Manager.

PLC Manager

The PLC Manager is a firmware component that loads the necessary PLC program code into the memory and controls all PLC-related components. The program code can exist of an IEC 61131‑3 program that was created and sent using PLCnext Engineer.

The code can also be created in C++ or MATLAB® Simulink®. C++ and MATLAB® Simulink® programs are available on the controller as program code libraries (shared object, *.so).

Configuration files on the controller are used to determine which libraries the PLC Manager is to load and which programs in these libraries are to instantiate. The PLC Manager is therefore superordinate to the code. It controls booting up and shutting down of the real-time system (ESM) as well as starting and stopping data exchange via fieldbuses.

If the controller is in the stop state, the real-time tasks monitored by the ESM are not executed. The signals of the sensors connected to the fieldbus are no longer read as inputs, and the output signals are no longer sent to the connected actuators.

The PLCnext Engineer software can be used to start the controller in three different modes:

  • Cold Start:
    During a Cold Start, all data is reset.
  • Warm Start:
    During a Warm Start, all data is reset and all retentive data is restored (system start).
  • Hot Start:
  • During a Hot Start, the data is neither reset nor restored. All variable values are retained.

PLC state

Available states

A PLC can be in one of these basic states:

Ready The firmware is set up but the PLC is not loaded.
Stop The PLC is loaded and set up but not started.
Running The PLC is started.
Halt The PLC is halted for debugging.

To get more information about the current state, search for PlcState in the API documentation of the firmware release you're working on. There you will find more information on state and error flags.

Changing the PLC state

The state of a PLC can be affected by the IPlcManagerService2 RSC service which can be used by C++ programs to call the respective Load(), Start(), Stop(), or Reset() function (see the PlcState diagram). These functions check if the PLC is in the initial state for the demand so changing the state is possible.

Even the PLCnext Engineer uses the IPlcManagerService2 for user operations. In addition, some errors (e.g. ESM task watchdog or exception) can cause changing the PLC's state from Running to Stop. 

Changing between the Ready, Stop, and Running state is done by the RSC serviceIPlcManagerService2 directly; changing between the Running and Halt state is done in the PLCnext Engineer.

Recommendation:

On calling the Load(), Start(), Stop(), or Reset() function the async parameter should be set to True. By doing so, the operation is executed asynchronous, immediately getting back and avoiding a timeout during the RSC call. Then the PlcState can be polled to check when the change is active.

Getting notified on PLC state changes

There are different ways to getting notified:

  • via IControllerComponent interface:
    PLM and ACF components can register with the IControllerComponent interface
  • via Notifications in C++:
    PlcState changes are logged as Arp.Plc.Domain.PlcManager.StateChanged notification, which can be subscribed at the NotificationLogger
  • via PLC events:
    ACF components can get notified on state changes by means of the PlcDomainProxy object (see API documentation). Therefore the components must create a function for each event coming into question. Each state change has two events that are triggered at the beginning and at the end of the event.  The functions have to be registered at the PlcDomainProxy by += make_delegate(), and unregistered in the Dispose() function of the component.

PlcState diagram
PlcState diagram

Reading the state of the PLC

The GetPlcState() method of the IPlcManagerService2 provides the Arp::Plc::Commons::Domain::PlcState enumeration as a return value. In this enumeration, the current state is combined with additional information bits.

  • With PlcState::StateMask the raw state can be extracted
  • With PlcState::FlagsMask the portion of additional information can be extracted (see the following table)

Additional information at PlcState

Hot The PLC is stopped in hot state, that is all data still remains, so a Hot Start is possible.
Warm The PLC is in Stop state and a Warm Start is possible. The retain data will be restored.
Loading The PLC is loading the Plc components. Available from firmware version 2023.6
Starting The PLC is starting the Plc components. Available from firmware version 2023.6
Stopping The PLC is stopping the Plc components. Available from firmware version 2023.6
Resetting The PLC is resetting the Plc components. Available from firmware version 2023.6
Changing The PLC is currently changing a configuration. This implies that the Running state is set. Designates the state during execution of Download Changes (PLCnext Engineer function: Write and Start Project Changes).
Forcing The PLC is in Force mode. One or more variables are forced by the GDS.
Debugging The PLC is in Debug mode. One or more breakpoints are set.
Warning An unspecified warning occurred.
Error An unspecified error or exception occurred, and the PLC is in STOP state.
Typically this error is caused by an erroneous PLC configuration. The PLC usually remains in Ready state; if not, the Reset() function needs to be executed.
After fixing the error the PLC has be set to the Stop state by executing the Load() function again, and thereafter the Start operation may be called so the PLC changes to Running state.
FatalError An unspecified fatal error or exception occurred, and the PLC is in Error state. The entire firmware has to be restarted.
From 2025.0:
SystemError 		This error bit is set if an unspecified fatal error or exception occurred and  the PLC is possibly in an inconsistent state. A typical cause of a system error would be an erroneous device configuration, or a binary incompatibility. The automation project on the PLC cannot be updated in this state. The firmware has to be restarted. 
Up to 2021.9:
SuspendedBySwitch
From 2022.0 LTS:
Suspended 		This error bit is set if the PLC could not be started because it was prevented by a component. For example, it is suspended by the hardware STOP switch that exists at some controllers.
Up to 2021.9: 
SuspendedBySystemWatchdog
From 2022.0 LTS: 
Blocked 		This error bit is set if the PLC could not be loaded because it was prevented by a component, e.g. the PLC has been suspended by a system watchdog. In this case a Cold Start has to be performed manually.
DcgFailed This error bit is set, if the PLC tried to perform a change operation, but an error occurred. This bit is usually combined with the Running state. Available from firmware version 2023.6 
(Dcg means Download Changes, in PLCnext Engineer the function is called Write and Start Project Changes.)
DcgNotPossible This error bit is set if the PLC tried to perform a change operation, but it was not possible. This bit is usually combined with the Running state.
(Dcg means Download Changes, in PLCnext Engineer the function is called Write and Start Project Changes.)
DcgRealTimeViolation This error bit is set if the PLC tried to perform a change operation, but it was not possible in real time. This bit is usually combined with the Running state.
(Dcg means Download Changes, in PLCnext Engineer the function is called Write and Start Project Changes.)
From 2022.6: 
StartingDelayed 		The PLC is about to start but due to component conditions the PLC start has to be delayed. Such a delay may be caused by an integrated Uninterruptible Power Supply (UPS) if during power up the UPS is not yet loaded sufficiently. 

 

 

• Published/reviewed: 2025-07-22  ⌨  Revision 082 •