External Interrupt Trigger level

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Hi

I've built a zero crossing circuit (using LM311) that will input the zero cross pulses into RB0/EXT pin of my 16F877 microcontroller.

What amplitude and width of a pulse can 16F877's external interrupt detect?

I looked in 16F877 datasheet but could not find it there.

Thanks.

[Haplo]

External interrupt on the RB0/INT pin is edge triggered. Figure 3-3 in the datasheet shows that RB0 has a TTL input buffer, so it is a TTL level logic (that means the input low voltage is 0 to 0.15VDD and the input high voltage is 2.0 to VDD, according to Table 15-2).

Keep in mind that the absolute minimum input voltage for almost all the pins (including RB0) is -0.3v.

[Ttelmah]

The 'active time' needed for an interrupt signal, on the 877, is parameter 22, in table 15-2. It is the instruction cycle time for the processor, but asynchronous (effectively the signal should be present for one complete instruction cycle, or it can be missed). remember that the timing starts, from the active 'high' level already given by another poster.

Best Wishes

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Thanks guys. I better look at the datasheet closely next time :D