This article will present Modbus resources to further aid the automation developer. The internet offers a wide variety of sites related to Modbus development from personal to commercial sites. This article will focus on two of the more detailed Modbus related websites.

The first website to be examined will be the official Modbus organization site, which offers a webpage specifically geared for the developer. The developer page on this site is divided into two categories:

• Modbus Technical Resources
• Offsite Links

The Modbus Technical Resources section of the developer page includes the following links:

• Current versions of Modbus specifications and implementation guides.
• The RFC link offers participation in the process of Modbus development.
• The Modbus Tool Kit link provides valuable developer resources. Products are free to corporate members, and at a price for others.
• The CTP link provides information for the developer to evaluate Modbus devices with the specifications.

The offsite links section of the developer page offers:

• The link allows the developer to compile with Visual C++ 6.0 with Windows 95/98/2000 support.
• FreeMODBUS offers the developer a no-cost implementation of the Modbus protocol, and is specially targeted for embedded systems. This implementation is based upon the most recent standards and should be fully standard compliant.
• Modbus implementation through a Java library. The site is geared towards Java developers that need to access or share data using the Modbus protocol. The library is fully object oriented, based on abstractions which should support easy understanding, reusability and extensibility. This library is a free and open source to the public.
• This link offers communication with Modbus/RTU slave devices connected to a PC serial port.
• Modbus Poll allows the developer to test Modbus slave devices. Modbus Poll is a shareware program that supports Windows 95/98/ME/2000/XP.

There are other links in this section of the webpage. Developers should closely examine this page for other information and products for their specific needs.

A page of the Chipkin Automation Systems (CAS) website is the second important resource for the Modbus developer. CAS is a premier building automation authority. The company’s primary focus is on system integration and protocol conversion.

The CAS Modbus Scanner provides the developer with a utility program for the retrieval and review of Modbus enabled device(s) in a wide variety of formats, and at no-cost to the developer.

Written by: Scott Cosby

© Chipkin Automation Systems 2007