The Design Of Soft Embedded PLC Virtual Machine Of IEC61131-3 Standard

Since middle of 20 century, the controllers that base on PC and embedded operation system are used on machine and automation equipments with the developing of technology of computer. Programmable logic controller (for short: PLC) becomes more important. Anew concept is proposed that soft embedded PLC virtual machine of IEC61131-3 standard. A new software platform is designed for the soft embedded PLC virtual machine. The software platform accords the IEC61131-3 standard and good expandable. It is a new thinking with the control system developing.The author proposed the new concept of PLC virtual machine by analyses the function of virtual machine and the specialty of PLC. The PLC virtual machine is abstracted from the traditional hard PLC. It is a soft platform that includes task scheduler and command system is independent of hardware. The PLC virtual machine manages the resource of hardware and software of PLC. PLC virtual machine is an embedded application. It is composed with software modules. All the modules release in dynamic link library and supply the header file for the interface. User can embed the PLC virtual machine into the control system and use the function of PLC by call the interfaces of software modules.The author researched the IEC61131-3 standard and created software modules for the ladder language of the standard. The data structure and function of the ladder elements are designed by the requirements of the standard. The author designed the data structure of ladder for storage and variable types, data types. An expandable library of the elements of the ladder is created.By the condition of the project, two tasks are designed for PLC. They are fast logical task and slow logical task. A schedule is designed between two tasks. Fast logical is a task that needs to be finished in time. So it will be call and be finished in each sampling cycle. Slow logical is a infinite loop task. So it will be run and finished in several sampling cycle.Object Oriented Programming is used for design to improve the flexible of software. The author designed a command system and interpreter. The command system includes 67 commands (please look attachment 1). All the commands are object. The multimode technology is used on them. The design improves the speed of the interpreter running PLC program. The commands can realize the Boolean calculation and function calling.