In the relay it is possible to activate up to five protocol server instances, each represented by a separate function block in the relay configuration. The five function blocks are named MBSLPRT1...5. For each connected client, a protocol instance has to be activated by dragging the function block into the relay configuration. When a function block is present in the configuration, its setting and monitoring parameters are visible in the HMI. An exception is protocol instance 1, which is always visible in the HMI, and which can be activated without dragging its function block instance into the relay configuration.
The protection relay restricts communication clients to five, regardless of the protocols that the clients use. This includes the MMS clients and other communication protocol clients.
The available five Modbus instances may be freely activated. However, it is recommended to activate the instances in chronological order. For example, instance 1 is to be used if there is only one client connection and instances 1 and 2 when there are two clients.
First setup and configuration upload
Dragging a protocol instance function block into the relay configuration is only the first step of the protocol activation. When a protocol instance is added for the first time, it is inactive and unconfigured by default, meaning that it has not been assigned to a physical link port. Neither has any Modbus data point configuration been loaded for the instance. Next step is to do these setups.
When a configuration containing Modbus instances is uploaded to the relay, the Operation setting is "Off". After the upload is done, the Modbus instances restart, still with Operation being in "Off" state. Thereafter, Parameter Setting in PCM600 uploads the new settings to all applications, including the Operation "On" values for the protocol instances. In this case the relay must be restarted once more in order for the Modbus protocol to start operating properly.