The Design And Application Of An Supervision System Among Different Minitype PLCs Based On CAN-bus

Field management informatization is the inevitable trend for small and medium-sized enterprise to keep competitive power. The main work of the paper is to establish an communication system between PC and different minitype PLCs utilizing the communication protocol embedded in mintype PLC of equipments and CAN field bus without changing current equipments. It can monitor the operating process of the equipments and achieves the goal of field management informatization with low cost.MC68HC908GZ60 MCU, an 8-bit micro-controller, produced by Freescale, is the main control chip in this monitor PCB board. This MCU is available with varieties of module, including RS232 serial communication interface, CAN bus interface. There are RS232 and CAN interface and power module in this board. Disturb and noise were fully considered during the design of hardware.There are two parts of software. One part is running on PC and the other is running on MCU. MCU software is divided into main control node and monitor node. The initialization of the system, the communication of CAN bus, the communication between main control node and serial communication interface can be achieved by the MCU software which has been written according to the embedded program standard. PC software is developed by means of facing objects and its interface including parameters setting, real time monitor and history record.After designed and tested in lab, this system has been debuged in a factory in Suzhou and the result is good. Below are the innovations in this subject: with the CAN bus technology, the communication has been achieved among minitype PLCs which can save lots of money for small and medium-sized enterprise; the self-define protocol of the communication system improves the validity and stability of the information transmission.