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Forum Index : Microcontroller and PC projects : A/D overflow on micromite

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robert.rozee
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Joined: 31/12/2012
Location: New Zealand
Posts: 2350
Posted: 06:07pm 29 Mar 2014
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a quick question for geoff:

what happens if the A/D converter in the micromite overflows? is this condition handled?

the obvious answer is that, as currently implemented, it can not (on the face of it) overflow. but what if it could due to external noise getting into the system? i'm particularly interested in the possibility of an overflow occurring while reading an analog input within a 10mS timer ISR, and if said overflow could create a delay situation (of tens of milliseconds) that may cause interrupts to be lost.


cheers,
rob :-)
 
JohnS
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Joined: 18/11/2011
Location: United Kingdom
Posts: 3815
Posted: 09:03am 30 Mar 2014
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I don't understand how it could? It's just a value in a range and that's it, isn't it? It can hit the end of the range, and stay there at worst - right?

John
 
robert.rozee
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Joined: 31/12/2012
Location: New Zealand
Posts: 2350
Posted: 07:07pm 30 Mar 2014
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most A/D converts will raise an overflow condition, and may require some sort of 'reset' be performed to recover. i have no knowledge of the details of the converter in the 32MX150, hence why i ask.

it would be undesirable for an A/D converter to peg at the top value, as it would then be producing a measurement that appeared to be valid, but that may be just a fraction of the voltage being applied.

hence, given the micromite appears to return 3.3 as the top value when an analog pin is tied to Vcc, a reading of 3.3 should be taken as an overflow. unless, of course, you already know that the volatge being measured lies between 0v and Vcc.


rob :-)Edited by robert.rozee 2014-04-01
 
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