4/2/2015 5:42 PM | |
Joined: 9/27/2006 Last visit: 4/23/2024 Posts: 12257 Rating: (2665) |
Hello mamadou; he following document has been written for the S7-300 PLCs, but the theory can be applied to the s7-1200 as well. It discusses hardware interrupt OBs, how to set them up and confiigure the IO modules that will be linked to one of the OB4x.
What is a hardware interrupt and how do they work in the S7-300 system?
If an alarm-triggering event occurs during program processing, the operating system calls the alarm OB 40, interrupting the processing of the program cycle or lower-priority program blocks. The alarm-triggering event (or events (multiple bits can be set)) is/are specified more precisely via the alarm OB 40's temporary local data. The temporary local data can be evaluated by the user program in the alarm OB. Basically, every OB recieves a priority level number (look at your CPU properties to see which OBs are available and what priority level it has been awarded by the operating system of the PLC). The lowest priority is attributed to OB1, which means that any other OB (with a higher priority number, by definition) will interrupt OB1 when the OS requires it into action. OBs (except for OB1) will run for a few milliseconds typically, and return control to OB1 once they have finished processing their runtime Of course this can extend the scan time of the CPU..If for any reason you get "stuck" in any function (OBs included) the watchdog timer will detect an overrun and stop the PLC. Hope this helps, Daniel Chartier |
This contribution was helpful to1 thankful Users |
4/3/2015 12:33 PM | |
Posts: 45 Rating: (0) |
thank's for your help :) (3) set filter time ? what does it mean ? why we tick enable rising edge detection instead of enable falling edge detection ? |
4/8/2015 5:30 PM | |
Posts: 45 Rating: (0) |
hello !plz.. why the OB40 doesn't set off after having a falling edge of i1.2 (see attachment) the programme rest always in ob1 !!! |
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