AVR-Chat

From: AVR-Chat@yahoogroups.com
[mailto:AVR-Chat@yahoogroups.com] On Behalf Of John Samperi
Sent: 18 May 2009 23:44 To: AVR-Chat@yahoogroups.com
Subject: RE: [AVR-Chat] Mega8 starting at wrong osc speed

> At 06:34 PM 18/05/2009, you wrote:
> > I do not have a cap on the reset line. Coming from 8051
> > designs, 
> 
> So how did the 8051 get the correct reset? A 8051 diagram
> in front of me uses a 1uF to VCC and a 22K to ground,
> (reverse logic of the AVR) also I believe that some 8051
> had something like a BOD so not much different. :-)   
> 
> I dare say that the reset circuit is the most important
> part of any design, regardless of the processor used,
> along with VCC bypass and proper clock circuitry, which
> seem to get overlooked the most.   
> 

My 8051 designs always had 1uF/10K like you say, so initially we started
off using that on the AVR, except the other way up obviously. But
through experience we found that the AVR started up much more reliably
without anything on the reset pin (sometimes just a pullup resistor
depending on if we were using ISP).

We were using Atmel 8051 (89C51 and 89C52) which did not have BOD or
anything like that. 

-- 
Tim Mitchell