Defining Bindings

Bindings are links, for example access paths, between variables located in different controllers belonging to the same project. Define bindings between variables of the same type. From a controller, bindings are defined as having a producer variable sending values to a consumer variable.

The controller consuming the data establishes a binding link with the controller producing the data. The controller also schedules sending and receiving data, sending diagnostic data, managing the safety response when faults occur, and managing communications redundancy.

When defining bindings, controllers must be connected via the SNCP (Safety Network Control Protocol) network. The SNCP network is a SIL 3 certified protocol supplying a safety layer for the Ethernet network. This diagram displays an SNCP network:

The controllers requiring a binding link must be physically connected to each other. The SIL rating of the communications interface is unaffected by the design of the Ethernet network, but the network reliability and spurious trip rate are impacted. SNCP network data can be combined on a common network resulting in safety and non-safety data sharing a physical network. The SIL rating is unaffected by using a common network, but introduces failure modes and possible security risks increasing the spurious trip rate.

SNCP networks can be configured as simplex (fail-safe) or redundant (fault tolerant). The network configuration depends on the application safety and availability requirements. Since the connection between controllers is treated as a logical network, sending and receiving data occurs independently from the physical network.

For individual controllers, variable binding definitions are available from both the producer mapping and consumer mapping perspectives. Example: View the

C1_Var1

(Producer) to

C2_Var1

(Consumer) binding between

Controller1

and

Controller2

from the Produce Mapping view for

Controller1

or the Consume Mapping section for

Controller2

.

Bindings use the parameters defined for the producer controller; parameters defined for the consumer controller are ignored. Multiple consumers can connect to a single producer. A single consumer can connect to multiple producers. A producer can also be a consumer and vice versa.

Variables are not updated in the consuming controller until the producing controller sends the values through the binding media:

The

AADvance-Trusted SIS Workstation software®

does not impose the read-only accessibility for consumed variables. To avoid conflicts between bindings and the execution of POUs, it is highly recommended to declare consumed variables with the read-only attribute.

Before defining bindings between controllers, create a link enabling the transfer of variable values between these controllers. For each controller, specify the Ethernet port allowing communication and the SNCP link properties.