View Full Version : looking difference between OB10 to OB17 & OB20 to OB23 of S7

January 15th, 2007, 06:14 AM
I am newbie in S7 PLC. Could anyone tell me with some example(easy ladder or statement programs)what is the difference between Time of day interrupt(OB10 to OB17) and time delay interrupt(OB 20 to 23. It would be very helpful if i get reply with examples, since from manual i can not understand how to use those blocks.


January 15th, 2007, 07:02 AM
Hello arocon;

Sorry I don't have any coded examples right now, but basically the difference is simple:
-You want to trigger an action every Monday, at 7:00 AM, starting January 1st 2007; for example, call the code in FB72. Use a Time-of-day interrupt for this. Program a network in OB10 that will set M1.0 (for example); parametrize the date and time you wish to have OB10 called by the operating system (through HWConfig, CPU parameters) or SFC28/30; load that OB10 into the CPU memory. Program and load FB72 as you like, making sure the last network resets your trigger bit M1.0.

-You want to ensure that there is a delay between one action and another, and you need the precision of the delay to be better than internal timers' capacities. For example, you need the delay to synchronize the start of a series of conveyor. Use a time-delay interrupt for this; use SFC32 to specify the delay you need, and set a bit in OB1 (for example) that will call SFC32; this will trigger the delay interrupt.

If I remember well there were examples of these interrupts (and more) iin the manual for Step 7 v. 5.2. They must be available in the newer versions.
hope this helps,
Daniel Chartier