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Sorry that I forget to point out (it was obviously for me) that the program does nothing sensible but it is just (minimal) example that using Wire library together with interrupts don't work in the provided example. I would like to thank you for all your answers! Now, what did you actually want it be doing? Turning off interrupts is also going to complicate things. This will cause the interrupt routine to increment puls but you don't do anything with it so I can't see how you know whether or not the clock is interrupting. If it does, and if you have the SQW signal connected to the correct pin, an interrupt will occur once every second. I think the RTC might, by default, output a 1Hz signal. This prints a message, turns interrupts on (why?), waits a second, turns interrupts off (WHY?) and prints another message (with interrupts off, maybe it doesn't print). It is also NOT a good idea to send to the clock so frequently because it will make the clock drift much faster than it would normally.
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This just tells the realtime clock that you are going to read or write to/from its register zero, but then you do neither.