Method to shorten the scan cycle of PLC program - Database & Sql Blog Articles

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Improve the efficiency of plc operation and shorten the execution time when completing the same task.
Reminder: Beginners don't have to care about the practices summarized in this article. They can read the program and read the specifications to complete the functional requirements.
1, you can use "words" when you try to avoid using "double words", you can use integers, try to avoid using real numbers.
2. Give priority to the use of IB, IW, ID, QB, QW, QD (other than hardware connection), followed by M, S;
3, try to avoid data type conversion, have to use, try to use AC to store intermediate variables, reduce the number of conversions. Or, when programming, first reserve the storage space. For example, when VW2 is used to store an integer, VW0 is not used, and the data in VW2 can be directly accessed in the form of VD0.
4. Reduce unnecessary network scanning, classify networks that can be conditionally executed (especially AIW, AQW) into subroutines for conditional calls (such as timed interrupts);
5, use XOR instruction to achieve arbitrary bit reversal (this instruction is slightly difficult, more need to be carefully aligned in debugging, binary number is recommended when programming);
6. Under the premise of ensuring the process requirements, appropriately reduce the frequency of interruptions;
7. The subroutine should minimize the number of conditional judgments, normalize the subroutine import and export parameters, and thus reduce code redundancy.
8. For repetitive and time-consuming tasks, sub-cycle processing should be used; this includes: apportioning the initialization work to multiple cycles. The sampling time of multiple PID loops is slightly different to avoid multiple interrupt calls in the same cycle, which makes the scan cycle more uniform and stable.
9. For subroutine calls with less input data, you can first determine whether the input data has changed. If there is no change (for comparison, refer to the 48th floor), you can skip the subroutine directly, thus reducing the scan cycle.
10. Try to arrange the bit variable in the V zone in V511.7, and arrange the VB/VW/VD variable with high frequency to be placed in V4095, which can shorten the program scanning cycle.
11. If SM0.0 is connected in series with other signals, it only increases the program size and execution time. There is no other function (if the network has already met the necessary contacts on the left side, it is not necessary to connect SM0.0 in series);
12. When there is no need to share signals, multiple instructions placed in the same network will generate additional inbound and outbound operations (which can be converted to STL for analysis), and if not logical, avoid horizontal in-line, which can at least reduce An "and" instruction. The benefit is just to put it in a network and feel a bit compact.
13. Reasonable use of the immediate IO command (to minimize use) saves the conversion time of the PLC processing immediate instructions.
14. Try to use the calculation result memory instead of the transition memory.