ABSTRACT
With the development of internet, communication and control techniques,
the domain of information communication and exchange has been covering from
the layer of equipment to the layers of control and management. The rapid
development of information technology has brought the transformation of the
structure of industry control system, and a new technique---Feildbus comes up.
However, because of the high cost at one time to the rebuilding based on
Feildbus and the monopoly by the foreign corporations, it is of great importance
for the popularization and application of Fieldbus in our country to develop the
digital meter based on Fieldbus which is suitable to the company in our country
and put it into production.
With the consideration of the fact in our country, this article introduces the
background and the status quo of Fieldbus. Furthermore, It brings up a Feildbus
resolvent in the industry control system.
This system is designed for a temperature-control industrial condition, and
the main control unit of the system is the digital meter. The digital meters and an
master consist of an industry control network in which the latter is used to watch
and configure the former, and the Feildbus technique is used to ensure the
speed and the reliability of data communication in system. In hardware, We used
Ultra-Low Power Microcontrollers---MSP430F149, whose rich resources and
powerful development tools can ensure the development schedule; Moreover,
the high precision AD---ADS1240 (24 bits )ensures the precision of data
collection; The liquid crystal display increases the mutual information
communication between the user and the system. In software, the designing
mode based on RTOS can improve the capability of the digital meter in real-time
and reliability, and greatly decrease the times that the system is down. Besides
that, the system is convenient to be configured. On the hand of Fieldbus protocol,
ModBus is given a particular explanation, and concrete realizing methods are
provided through which communication as a separate task is running on the
kernel of RTOS and the real-time and reliable of data transmission are assured.
Besides that, ModBus protocol are improved and extended, and a multi-host
network system based on virtual token is provided and proves well. The
computer is used to simulate the ModBus master to watch and configure the
control unit using the technique of multithreading and database. The computer
program can be conveniently rewrote as a bridge software, through which the
above industry control network can be connected to other networks, at the same
time it provides foundation for the further study of Fieldbus.
Practice proves that this system is robust and reliable. The project reaches
its design requirement, and provides a quite new solution. In fact, its practical
performance in market is satisfying both in economic and in social benefit.
Key words: FieldBus, MCU Control, RTOS and Modbus Protocol