Overview of Logical I/Os
Principle of the logical I/Os
The logical I/Os serve the exchange of data between the standard and safety controllers. Two types of data can be exchanged: global variables and I/O data. The safety controller itself has no I/O data. These must be configured in the standard controller and then exchanged with the safety controller as logical I/Os.
If an I/O module with safe I/Os is inserted in the controller configuration in CODESYS, then a matching logical I/O is automatically inserted in the safety controller (same name as the I/O module on the standard side). This logical I/O contains all safe I/O channels as well as the safety parameters of the module, so that all safety-relevant information can be found under the safety application.
The logical I/Os of the safety application are linked to the default application with physical devices or Logical Exchange GVLs (special object on standard side). This means that there is precisely one logical I/O in the safety application for each physical device whose input/output signals are processed in the safety application. Likewise, precisely one logical I/O exists under the safety application for each GVL for the logical exchange of the standard controller. The assignment is variable.
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The fail-safe parameters of a device whose inputs/outputs are processed in the safety application can be edited only in the appropriate logical I/O in the safety application.
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The descriptions of the logical I/Os are managed in the Logical devices category of the Device Repository.
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For a better overview, folders can be added to the project tree under Logical I/O in order to group the logical I/Os.
Notes on the logical I/Os
The logical I/Os are assigned depending on the name of the application and the logical I/O object. This gives rise to the following notes:
If the name of a logical I/O is changed, then the name of the physical device or the Logical Exchange GVL must be automatically tracked so that it does not have to be reassigned to the logical I/O.
The renaming (except in the case of "default assignment") or relocation of field devices in the device tree or of Logical Exchange GVLs in the main application does not change the assignment to the logical I/O in any way. The safety application is changed automatically when it is renamed: The assigned logical I/O is renamed the same as the field device.
If the field device is shifted into a different parallel controller, then the link is dissolved and the field device must be reassigned to the logical I/O of the safety application.
The deletion of the field device from the device tree or of the Logical Exchange GVL from the default application means that the assigned logical I/O can no longer be mapped to anything (no longer supplied).
The deletion of the logical I/O object means that fail-safe settings are no longer mapped to the field device or that the "from Safety" variables in the Logical Exchange GVL are no longer supplied.
If a different logical I/O object is given the old name of a renamed or deleted logical I/O object, then from now on its settings are mapped to the assigned field device or its variable values are exchanged with the Logical Exchange GVL. The assignment is thus indirectly changed.
If a logical I/O has been deleted and a new logical I/O is inserted with the name of the deleted logical I/O, then the assignment is active again.
If a physical I/O object that is linked with a logical I/O object is copied, then the logical I/O object is also copied together with its data.
Advantages of the logical I/Os
The concept of the logical I/Os gives rise to the following advantages for the development and verification of a CODESYS Safety Extension safety application:
The parameterization of the safe parameters of field devices (e.g. F-parameters in PROFIsafe) takes place only into the logical I/Os of the safety application. If safety user management is set up, this parameterization can only be done by members of the Safety user group.
Changed assignments of physical field devices and Logical Exchange GVLs do not change the safety application, since the changes of assignments take place under the main application (standard application) and become effective by downloading to the standard controller.
A pre-verified and accepted CODESYS Safety Extension safety application can be detached from the original project and integrated completely in a different project without this new safety application having to be verified again. When doing this suitable field devices and Logical Exchange GVLs must be reassigned to the logical I/Os of the safety application.
Object properties
The properties dialog is opened by selecting the corresponding logical I/O in the project tree and clicking the Properties command in the context menu. It contains the following tabs:
Common (for a more detailed description, see: Object properties)
Safety
Access Control (for a more detailed description, see: Object properties)
The properties dialog of all logical I/Os contains the Safety tab in addition to the Common and Access Control tabs.
Safety CRC
CRC for the logical I/Os
Safety CRC (CNF) (if aspect Safe configuration available, see Tab: Safe Configuration)
Safety CRC (PAR) (if aspect Safe device parameterization available, see Tab: Safe parameterization)
Version (editable)
The developer can freely assign the version. The version can be used for quickly detecting the object version in the object list of the safety application object.
Comment: A comment for the logical I/O can be entered here.
Editor of the logical I/Os
For a detailed description of the editor and its tabs, see: Device Editor of Logical I/Os