Re: [avr-gcc-list] newbie trying to get at90s8515 to work on breadboard

[Chris Donovan]

> > I don't have either XTAL1|2 connected to anything at the moment.
> >
> > Ok so basically I have the following:
> >
> > +9V --> 410ohm --> pin40(VCC)
> > pin20(GND) --> -9V
> 
> I assume you mean the negative side of a 9V supply - that's 0V, -9V 
> would be if you had an 18V supply.

Yes, that is exactly what I meant 0V.

> > pin1(PB0) --> 40ohm --> LED(2V)
> with the other end of the LED to GND?

Yes it is connected to the 0V.

> 2V,20mA LED means the resistor has to drop 3V. V=IR, so
> R=V/I,
>  =3/0.02 = 150 ohms

I am putting 5V into the pin40(VCC) and it seems to come out right at 2V
which is exactly what the specs say is within the minV and maxV amounts
(3mm diffused LED).

> It will light with 460 ohms, but dimly.
> 
> RESET should be pulled high with a resistor, somewhere around 500-2K, 
> the exact value doesn't much matter.

What does pulling it high mean, and what is the purpose of that?  I
haven't done this part yet but I did the below steps(adding a crystal,
and 2 33pf caps) and it is working just fine(to me of course).

> >
> > When I connect the GND the LED goes out but when disconnected the
> > LED is on, and I don't exactly understand why as yet.
> 
> The chip is not running, every part of it is at +5V, including the 
> output pin. When you connect GND the chip starts to work, and grounds 
> the LED output.
> 
> I like 3 pin ceramic resonators. You just connect the outside pins to 
> XTAL1 and XTAL2 and ground the centre pin. Dead easy, and no
> capacitors to worry about. I wouldn't worry about oscillators, they're
> expensive and not as straight forward to use as they sound. Don't get
> two pin resonators though; they still need capacitors, you might as
> well use a crystal. If your application needs exact time-keeping then
> you need a crystal. Be sure to fit exactly the right capacitors for
> the crystal you buy.

I have it working now.  I connected a 4Mhz crystal to the pins XTAL1 and
2 , and then from each of those connected a 33pf cap from there to the
GND.  I know I should be using a 27pf (at least examples on the net
show those being used for a 4Mhz crystal) but so far it hasn't broke
anything by using the 33pf.  So basically it looks like this:

XTAL1 --> crystal1 --> 33pf --> \
                                 --> GND
XTAL2 --> crystal2 --> 33pf --> /

I really appreciate everyone's time and help for this seemingly simple
step for me.

Thanks,

Chris-