Application Layer for Bitbus Based Low Cost Technological Network

Abstract

Effective use of automation resources requires that they are interconnected by a communication system. To interconnected field devices such as sensors, actuators and intelligent process controllers; Fieldbus is used. The main idea of Fieldbus is to replace point to point links from each sensor or actuator to it's controller by a serial communication system. In this article we present the field bus from the application layer point of view. Experimental testbed of system consists of some sensors, actuators and PC machines. As a communication network Intel's Bitbus was chosen. Distributed system is based on the architecture of standard host PC with Master Bitbus controller and many remote slaves Bitbus modules (max 250). Each slave module represents microcontroller i8344 with on board memory RAM, EPROM, serial communication interface RS-485 and 8-bit PC-BUS extension which allows controlling of many standard I/O industrial PC cards. PC operates as an extension of a master node. When compared to other commercial field buses, it is seen that Bitbus is at least near enough the I EC standards requirements. Practical experience performed on experimental system have shown that commercial Bitbus software library is cumbersome and is not well suited for hard real time applications. Therefore new software modules were implemented in order to fulfill distributed real-time constraints. The flexibility of the microcontroller i8344 allows to implement specialized Logical Link Control sublayer and a Application layer.