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Re: [AVR-Chat] Problem with Atmega128 reset line

2004-08-28 by Ivan Vernot

The pull-up should be fine. Personally I would still use a 'reset chip'
(like the MC34064) to give a bit more margin for noise etc, but the 1K
should still work.

Something to check though is that Pin 1 (PEN) should be pulled up also.
HTH
Ivan Vernot
realtimedesigns

----- Original Message -----

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From: "Yang Wang" <yang_w2000@hotmail.com>
To: <AVR-Chat@yahoogroups.com>
Sent: Saturday, August 28, 2004 4:20 AM
Subject: [AVR-Chat] Problem with Atmega128 reset line

> Hi all,
>
> Can we connect the reset line and +5V line with a 1k pull-up
> resistor, to keep the reset line high? Out of the 8 circuit boards
> with the same schematics I am building, 6 of them work in this way,
> while the other two do not. For these two problematic ones, the reset
> line is always jumping between 2.1V and 4.7V, not stable at all.
>
> I feel like this 1k pull-up resistor setup should work for keeping
> the reset high. Or am I wrong, and do I have to connect the reset
> line with +5V directly?
>
> Thanks a lot!
>
> Yang
>
>
>
>
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Re: Problem with Atmega128 reset line

2004-09-01 by Yang Wang

Thanks for the reply. Do we have to pull up the PEN pin? I didn't 
connect it to anything, and it was high as I measured when the 
program was running, so it looks like it has an internal pull-up. But 
I think this is probably going to be worth of a try.

This is what I found on the datasheet, although it doesn't remind
about pulling up PEN at all:
PEN is a programming enable pin for the SPI Serial Programming mode.
By holding this pin low during a Power-on Reset, the device will
enter the SPI Serial Programming mode. PEN has no function during
normal operation.

Thanks a lot,

Yang

--- In AVR-Chat@yahoogroups.com, "Ivan Vernot" <ivernot@o...> wrote:
> The pull-up should be fine. Personally I would still use a 'reset
chip'
> (like the MC34064) to give a bit more margin for noise etc, but the
1K
> should still work.
>
> Something to check though is that Pin 1 (PEN) should be pulled up
also.
> HTH
> Ivan Vernot
> realtimedesigns
>
>
> ----- Original Message -----
> From: "Yang Wang" <yang_w2000@h...>
> To: <AVR-Chat@yahoogroups.com>
> Sent: Saturday, August 28, 2004 4:20 AM
> Subject: [AVR-Chat] Problem with Atmega128 reset line
>
>
> > Hi all,
> >
> > Can we connect the reset line and +5V line with a 1k pull-up
> > resistor, to keep the reset line high? Out of the 8 circuit boards
> > with the same schematics I am building, 6 of them work in this
way,
> > while the other two do not. For these two problematic ones, the
reset

Show quoted textHide quoted text

> > line is always jumping between 2.1V and 4.7V, not stable at all.
> >
> > I feel like this 1k pull-up resistor setup should work for keeping
> > the reset high. Or am I wrong, and do I have to connect the reset
> > line with +5V directly?
> >
> > Thanks a lot!
> >
> > Yang
> >
> >

Re: [AVR-Chat] Re: Problem with Atmega128 reset line

2004-09-02 by Brian Dean

On Wed, Sep 01, 2004 at 05:14:11AM -0000, Yang Wang wrote:

> Thanks for the reply. Do we have to pull up the PEN pin? I didn't
> connect it to anything, and it was high as I measured when the
> program was running, so it looks like it has an internal pull-up. But
> I think this is probably going to be worth of a try.

Figure 22 on my copy of the datasheet (Page 48) shows an internal
pull-up on PEN to Vcc, so you can safely leave PEN unconnected if it
is not used.  Also, for example, see the datasheet for the AT90CAN128
which is a "pin compatible" device and describes that pin position as
NC (Not Connected, leave unconnected - may be used in a future
revision).

-Brian
-- 
Brian Dean
http://www.bdmicro.com/