Command Login

Symbol: Command Login 1:

Function: This command connects the programming system (the selected PLC project) with the target system (controller) and thus establishes online operation. An instance of the PLC project is created on the target system and loaded.

Call: PLC menu or TwinCAT PLC toolbar options or context menu of the PLC project object (<PLC project name>Project) in the Solution Explorer

Requirement: The PLC project is error-free and the target system is in Run mode.

Possible login situations:

The PLC project does not yet exist on the controller: You will be prompted to confirm the download.
The PLC project is already on the controller and has not been changed since the last download. Logging in takes place without further interaction with you.
The PLC project is already on the controller, but has been changed since the last download.
You will be prompted to choose one of the following options:

At this point you can also update the boot project on the controller.
An unknown version of the PLC project is already on the controller. You will be asked whether TwinCAT should replace it.
A version of the PLC project is already running on the controller. You will be asked whether TwinCAT should nevertheless log in and overwrite the PLC program that is currently running.
The PLC program on the controller is currently stopped at a breakpoint. You have logged out and changed the program: TwinCAT warns you that, in the event of an online change or download, the PLC will be completely stopped. This happens even if there are several tasks and only one of them is affected by the breakpoint.

Compiling the project before logging in

If a PLC project has not been compiled since its last change, TwinCAT compiles the project before logging in. This operation corresponds to the command Compile in logged-out state.

If errors occur during the compilation, a message dialog appears. The errors are displayed in the Error List view. You can then decide whether you want to log in without loading the program onto the controller.

See also:

Command Build PLC project

Error on login

If an error occurs while logging on to the controller, TwinCAT interrupts the loading process with an error message. The error dialog allows you to display the error details. If an exception error has occurred and the text *SOURCEPOSITION* is contained in the log message, you can use the command Display in Editor to display the relevant function in the editor. The cursor jumps to the line causing the error.

Output of information on the loading process

If TwinCAT loads the project onto the controller when logging in, the following information is displayed in the message window:

Generated code size
Size of global data
Resulting memory requirement on the controller
A list of the affected function blocks (for online change)

	In online mode, you cannot change the settings of devices or modules. To change device parameters, you must log the PLC project out. Depending on the bus system, there may, however, be some special parameters that you can change in online mode.

	TwinCAT stores the view configuration separately for online and offline mode. In addition, views that cannot be used in an operation mode are closed. For this reason, the view may change automatically when you log in.