Modbus Implementation over ARM Cortex-M

Abstract

Nowadays, embedded systems cover a high percentage of the computer market, thus they are deeply inmersed in the current society, as in mobiles phones, kitchens, televisions, cars, planes, etc. Therefore, it is important for a computer student to acquire a background about such systems to have a good knowledge spectrum. The following work can be placed in the area of the industry world, where embedded systems are definetely present too. Concretely, they can be useful when certain constraints have to be met, as size, real-time, throughput, etc... To make possible these requirements, depending on the scenario, a proper communication has to be made between the elements of the system, and hence, a communication protocol is needed to establish the rules of the communication. This project consists in a definition of a new layer for a communication protocol standard called Modbus, and also, the implementation of it over ARM Cortex-M. The project is the extension of a previous work from another student, which was about the implementation of the Modbus protocol over ARM Cortex-M using over serial line, OSL, as physical layer and RTU as codification. In the former project, it was implemented OSL next to RTU to make possible a proper communication, and also, the application layer to process the data. That work follows the Modbus protocol standard, which it supports or is made to "natively" work with OSL and TCP, as these layers are defined and specified by the standard. Otherwise, in the present project the new layer CAN is defined firstly, as it is not supported nor defined natively by the Modbus standard. After that, the implementation is done over ARM Cortex- M to make the communication and transfer data to the application layer instead of using OSL and TCP. The following report covers the basic concepts and explanations about Modbus protocol, ARM Cortex-M, CAN bus and the implementation itself.