The values of certain SIS module parameters may be changed, via messages, from several workstation applications. In addition, commands (such as Unlock) may be sent to a Logic Solver via messages from several workstation applications. These messages travel through several layers of communications before arriving at the destination. It is necessary to have a mechanism that validates these messages before they are acted on by the safety system.
The Secure Write Mechanism, which is TUV-certified software, provides the validation of messages. The purpose of the Secure Write Mechanism is to substantially reduce the risk of sending an invalid message to the safety system from workstation applications. Secure writes are the only way that you can send write requests from workstations to SIS modules and Logic Solvers with the exception of writeable SIS alarm fields and SIS function block parameters of the string data type. Writeable SIS alarm fields and SIS function block string parameters accept standard writes.
The Secure Write mechanism:
Checks for security privilege to make the change
Provides a confirm dialog to allow you to verify the change request
Checks for message corruption
Checks that the message arrives at the intended destination
Prevents a spuriously generated message from causing a change
You must confirm that a change request is correct. You may press the Confirm button to continue with the change, press the Cancel button to cancel the change, or do nothing and allow a timeout to cancel the change.