1. Introduction
Each LUFP7 Profibus-DP / Modbus RTU gateway allows one of the PLCs on the Profibus-DP network to command, control and configure up to 8 Modbus slaves. Other Profibus-DP masters on that same network can only control them. If there are more than 8 Modbus slaves, you will need to use an appropriate number of LUFP7 gateways. In the same way, if the exchanges with the Modbus slaves require more than 25 Modbus commands (that is to say more than 50 queries and responses), you will have to distribute the Modbus slaves over several gateways.
The LUFP7 gateway behaves both as a Profibus-DP slave on the upstream network and as a Modbus RTU master on the downstream network.
See chapter 7.2 Communication Characteristics, page 86 if you would like to read about the technical communication characteristics of the LUFP7 gateway.
The gateway can carry out its data exchanges (inputs and outputs of all types) with the Modbus slaves cyclically, aperiodically or in an event-driven way. All of these Modbus exchanges make up the gateway’s “Modbus scanner” and we use the “ABC-LUFP Configurator” software application to configure this scanner’s exchanges. Every data element exchanged in that manner is made available for the Profibus-DP master, who may access it on a periodic basis. The only aperiodic interchange possible with the LUFP7 gateway is the explicit Profibus-DP diagnostic interchange.
The diagram on the left page illustrates the distribution of several slaves throughout three Modbus RTU downstream networks, each one being interfaced with the Profibus-DP master PLC using a LUFP7 gateway.
1.7. Principle Used to Configure and Operate the LUFP7 Gateway
The gateway is part of a family of products (referred to as LUFPz) designed to meet generic needs for connection between two networks using different communication protocols.
The software elements common to all these gateways (a configuration tool known as “ABC-LUFP Configurator” and the on-board Modbus software) cohabit with the specific features of the network upstream of each of them (Profibus-DP in the case of the LUFP7 gateway) generically. This is one of the reasons why the interfacing between the upstream network and the Modbus network is carried out entirely via the gateway’s physical memory.
ÖThe exchanges between the gateway (which operates as a Modbus master) and the Modbus slaves are wholly configured using the “ABC-LUFP Configurator”. This configuration tool goes into great detail (setting timers for exchanges, communication modes, frame content, etc.), which makes it all the more delicate to use. So a whole chapter in this guide (chapitre 6 Configuring the Gateway, page 44) has been devoted to this tool.
By configuring the queries and responses for Modbus commands via this tool the user can create links between a part of the content of the corresponding Modbus frames and the content of the gateway’s physical memory (input memory for the content of the Modbus responses and output memory for the content of the queries).
ÖThe exchanges between the Profibus-DP master PLC and the LUFP7 gateway should be configured in such a way that the Profibus-DP master can read the input data and write the output data from the gateway, but only the data used for the Modbus exchanges (see previous point).
