Modbus Application Overview

This section describes how to build an application for the HCC2 from the example source code using Modbus as the integration mechanism¹. This procedure assumes that the sample code is downloaded and installed as described in this section. The high-level architecture of the app created with the sample code is presented below.

The application structure is based on the following building blocks (see corresponding numbers above):

1. The application includes a Modbus TCP Client. This client periodically scans data and issues writebacks to a Modbus Server available as part of the HCC2 core software.

2. Scanned data are stored in a real-time memory storage that is also part of the application. Likewise, data written to the memory storage are written back to the HCC2 Modbus Server.

3. The application has access to read/write data from/to the memory storage using these API methods:

   • For Python

     get_value(tag_name)        - gets the last scanned value of tag_name (where 'tag' implies a 'data point')
     set_value(tag_name, value) - sets (writeback) a value on that tag_name.
     

   • For C#

     GetValue(tag_name)        - gets the last scanned value of tag_name.
     SetValue(tag_name, value) - sets (writeback) a value on that tag_name.
     

4. The HCC2 Modbus Server must be properly configured to accept queries and writebacks from the application.

The following sections will describe each one of the above steps.