Interrupt 'response speed'

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Francis
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Interrupt 'response speed'

Post by Francis » Thu Nov 18, 2010 10:48 am

I can't find anything under search and I'm currently scopeless (and hopeless).

With regard to a typical hardware interrupt (external source, change on portb for example); what is the minimum duration of an external pulse required and is there a rule-of-thumb related to clock frequency?

Jerry Messina
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Post by Jerry Messina » Thu Nov 18, 2010 11:29 am

In general, it usually is related to the system clock frequency, but that really depends on exactly which device you're talking about and which peripheral.

For example, the PortB change interrupt is usually spec'd at a min of Tcy (4 x Tosc), while external INTx signals on some devices are spec'd at a min high/low time of Tcy, and on others at a fixed 20ns. Other peripherals have completely different requirements.

You should really look at the AC Characteristics tables in the datasheet of the device you're using.

Francis
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Post by Francis » Thu Nov 18, 2010 11:41 am

Thanks Jerry. I couldn't see the response spec in the Data Sheet (I did look first, honest Guv).

I'll polish my specs and have another look.

Jerry Messina
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Post by Jerry Messina » Thu Nov 18, 2010 12:30 pm

Yeh, sometimes it's hard to find what you're looking for in all those specs. Also, it's not uncommon for specs to be left out of one datasheet, or for it to be "preliminary" for years. They've gotten a bit better over time, but there's some chips I use that I don't expect to ever see a "final" datasheet.

The bad thing is that they're constantly changing the peripherals from chip to chip, so you never really know what you've got, or if chip A is actually identical to chip B.

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