Hot-standby Embedded Controller System On The DeviceNet Fieldbus

The DeviceNet fieldbus based on the CAN was brought forth by the Rockwell in 1994 and became a kind of equipment-level network standard. Because it can provide the reliable connection and communication for the industrial field devices, the DeviceNet fieldbus has been widely used in the field of industrial control. As the most important part of the network control system, controller has to face the harsh field environment. Therefore its reliability is directly related to continuous and stable operation of the control system. In order to enhance controller's reliability, many manufacturers are developing hot-standby controller system based on fieldbus. Moreover most of PLC products based on the DeviceNet provide hot-standby function in the hardware redundancy way now, such as Rockwell's FlexLogix system.The topic of this paper is building a hot-standby embedded controller system on the DeviceNet fieldbus. The way is adding hot-standby software and heartbeat communication for dual controllers developed early. Firstly, presents that how this hot-standby controller system works and then explains in detail hot-standby strategy between dual controllers. Secondly, elaborates status recognition, standby controller's cutting-in, scanning cycle synchronization between a pair of controllers and fault controller's cutting-out in the hot-standby system, then makes task partitioning to hot-standby software and gives relationship between tasks. Finally, designs particular heartbeat-communication protocol between two controllers.According to forementioned design decision, codes on the experimental platform to model the operation of dual–controller system. In the experiment, tests several essential performance requirement for the hot-standby controller system, including status recognition, scanning cycle synchronization between dual controllers, standby controller taking over working controller and fault controller cutting in after restoring . The test proves that the whole design is feasible.