AD908JQ are pressure control (loop control) tasks, which have scan times of 1 ms and 2 ms, respectively, while C and D are logic control tasks, which have scan times of 5 ms and 2 ms, respectively. it appears that this is a PLC/PCC application with a large program volume of logic control tasks. Figure 1 represents the operation mode of a conventional PLC. In the task combination approach in the upper part of this figure, the whole task (A+B+C+D) is contained in a cycle with a scan time of 10 ms, and in the task combination approach in the lower part of this figure, the whole task (A+B+C) is contained in a cycle with a scan time of 8 ms. As can be seen, the total application processing cycle is the sum of the programme scan times of the individual tasks, and the programme is executed cyclically week after week.

The AD908JQ system design solution perfectly solves this problem. Compared with conventional PLCs, the most important feature of the PCC lies in its introduction of several types of mainframe computer Runtime qualitative time-sharing multitasking operating system concepts, supplemented by a variety of means of application software design. Due to the implementation of time-sharing multi-tasking operation mechanism, applications can be set into different tasks and different task levels in accordance with the different process functions and priorities.