Synth-DIY Yahoo! Groups Archives

Thread

Problem with Atmega128 reset line

2004-08-27 by Yang Wang

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, but I cannot find out why the reset line is not 
stable when it is connecting to +5V by the 1k resistor. Or am I 
wrong, and do I have to connect the reset line with +5V directly?

Thanks a lot!

Yang

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

2004-08-27 by Lasse Madsen

Hi Yang..

If you look at the ATm128 datasheet over the Reset line you will find no reason why the mentioned thing should occur…

A badly designed power supply comes to mind … try adding a large capacitor to your +5V and at least 100nF to Reset ..

Regards

Lasse Madsen

-----Original Message-----
From: Yang Wang [mailto:yang_w2000@hotmail.com]
Sent: 27. august 2004 20:25
To: AVR-Chat@yahoogroups.com
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, but I cannot find out why the reset line is not
stable when it is connecting to +5V by the 1k resistor. Or am I
wrong, and do I have to connect the reset line with +5V directly?

Thanks a lot!

Yang

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

2004-08-28 by Brian Dean

On Fri, Aug 27, 2004 at 06:24:37PM -0000, Yang Wang wrote:

> Can we connect the reset line and +5V line with a 1k pull-up
> resistor, to keep the reset line high?

Yes, that should be fine.  I normally use a 10K pull-up, but 1K should
work.  You don't usually want to to tie the line directly to 5V - if
you want to program the chip in-system, the programmer must pull the
reset line low, and it can't do that if you tie the line directly to
5V without a resistor in between.

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