Atmeg8 power-up reset reliability

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JohnPsmith
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Posted by JohnPsmith: Thu. Aug 21, 2008 - 04:35 PM
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I'm wondering what the experience of others has been so far as relying on the on-chip power-up reset. I've noticed that Olimex uses a Zetex supply monitor on at least one of their AVR boards...., makes me wonder. I suppose that in their case, they can't be sure what the programmer may do...., or the initial state of the internal reset mechanism. At any rate, I'd like to have the reset pin available as I/O....., so my question is: What has been people's experience as far as the best combination of reset parameters to assure reliable start-up?

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AVR Microcontrollers, megaAVR and tinyAVR
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Kleinstein
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Posted by Kleinstein: Thu. Aug 21, 2008 - 08:10 PM
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There should be no problem with power on reset when the internal brownout detector is enabeld. Worst case one could get a brownout reset instead of power-on, but usually one does not care about this detail.

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Bronze Marktheusch
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Posted by theusch: Thu. Aug 21, 2008 - 08:14 PM
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Quote:

At any rate, I'd like to have the reset pin available as I/O.....

??? So then the question becomes moot, doesn't it? You can't use an external reset controller then anyway, and need to rely on internal parameters for startup and brownout.

Lee

You can put lipstick on a pig, but it is still a pig.

I've never met a pig I didn't like, as long as you have some salt and pepper.

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Jepael
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Posted by Jepael: Thu. Aug 21, 2008 - 09:02 PM
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And while the reset pin is GPIO, you can't reset the part for ISP programming. I guess then you can use JTAG to program, but hey, I guess you don't have JTAG available if you are running out of pins anyway.

The internal Brown-Out Detector (BOD) is usually good enough if you need one. But if you have very slowly rising supply voltage, it might not be fast enough, and you need an external reset.

- Jani

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JohnPsmith
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Posted by JohnPsmith: Fri. Aug 22, 2008 - 04:18 AM
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theusch wrote:
Quote:

At any rate, I'd like to have the reset pin available as I/O.....

??? So then the question becomes moot, doesn't it? You can't use an external reset controller then anyway, and need to rely on internal parameters for startup and brownout.

Lee

Lee,
Therein lies the distinction between between "I'd like to..", and "I have to.." :wink:

John

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