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[DPRG] atmel reset

Subject: [DPRG] atmel reset
From: Earl Bollinger earlwbollinger at attbi.com
Date: Thu Feb 27 07:12:01 CST 2003

I think I figured it out. Several things affected it.
1.) It turns out the .1 caps I used are mislabled, no telling what values
they really are.
I changed them out using known good caps whose values have worked well
before. Surface mount caps
always suck as they all aren't marked or anything, and they all look pretty
much alike.
Of course the supposedly bad ones might be 500v or 1000v caps which has the
same affect of making
them look bad. Swapping out the caps made a world of difference.
2.) Every once in a while it would still pick up a glitch like power up
problem, so I tied the reset line to Vcc and that problem is crudely
eliminated. Item three would take of this also.
3.) Using the DC-DC converter is a new item for me, I probably should have
put in a "supervisor" IC to monitor the voltages and hold the MCU's reset
line low until power rises above a certain level. That might take care of
the little glitches too, as the "supervisor" IC would help in that area too.
But then that's how we learn. But to use it correctly I would need to design
it in on the PCB to start with, as there is little spare room in that area
of the PCB to kludge one in.
Here is a ref to supervisor IC's, several IC companies make them.
These little devices can save a lot of hassles in making MCU's work

Thanks to all for your advice.

-----Original Message-----
>From: Kipton Moravec [mailto:kip at kdream.com]
Sent: Wednesday, February 26, 2003 9:36 PM
To: Earl Bollinger
Cc: DPRG List
Subject: Re: [DPRG] atmel reset

According to the diagram of the capacitor discharges the board goes to
Put a 1K resistor on the reset line where it goes to the programming cable.

You also need to pull-up the other lines that you are using with the program
cable with a 10K.

Try that.

----- Original Message -----
>From: "Earl Bollinger" <earlwbollinger at attbi.com>
To: <dprglist at dprg.org>
Sent: Wednesday, February 26, 2003 9:13 PM
Subject: RE: [DPRG] atmel reset

> No reset switch is used for these PCB's, I could have put one on, but I
> out of space.
> The reset is only for the programmer to get the MCU's attention so it
> can reprogram it. Thus it only connects out via the ISP connector.
> Check out http://www.atmel.com/dyn/resources/prod_documents/DOC1619.PDF
> about the Reset Pin Protection section.
> Anyway it acts as though some kind of noise spike is causing the reset
> to go low long enough to
> cause the MCU to reset itself.
> -----Original Message-----
> From: dprglist-admin at dprg.org [mailto:dprglist-admin at dprg.org]On Behalf
> Of Frank & Gail Elia
> Sent: Wednesday, February 26, 2003 3:57 PM
> To: dprglist at dprg.org
> Subject: [DPRG] atmel reset
> Hey Earl
> I'm not following the logic of a bad cap. As I understand it the cap is
> to debounce the switch. When I breadboard I don't bother with the cap and
> just use a momentary switch with a resistor to ground. After all a bounce
> makes no difference since it will settle down and reset.
> Am I missing something?
> Frank
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