Electronics > Electronics
External clock and AREF connection for my augmented board ?
Robo73:
Hi all,
This is my first time to write in this forum. First of all, I'd like to thank those who are developing this website
for their great contributions. It's one of the nicest robotics websites I've seen.
Now back to my question. I actually have two questions. Basically, I'm building my own development board
using ATmega32 chip. Since I'm experementing at this time, I just want to have one digital port, and 4
analog pins, besides of course the ISP header for programming. Very basic.
[1] Now my first question is regarding the external crystal. I believe the chip comes with internal clock which I
think is 1 Mhz. I have a 4 Mhz clock that I'd like to connect to the chip, and here are my questions:
a. How to connect the crystal to my chip ? It has two leads.
b. If I connect it will there be an interference between the external and internal clocks?
c. I've seen crystals that come in different shapes and numbers of leads. For example, I've seen one
that comes in a DIP chip. How would the connection be different?
[2] My second question is regarding the AREF pin. PORTA is an analog port and I only need 4 pins. Now, I
remember I've read in the tutorial that AREF should be connected to AVCC. Should that always be
the case? When I need Not connect AREF to anything? here are the descriptions I found in the datasheet:
" AVCC is the supply voltage pin for Port A and the A/D Converter. It should be externally
connected to VCC, even if the ADC is not used. If the ADC is used, it should be connected
to VCC through a low-pass filter."
" AREF is the analog reference pin for the A/D Converter."
For the low-pass filter they're referring to, is is just a capacitor and resistor? what should their values be?
That's all I have for now. Thnx in advance.
Robo
Robo73:
It's ok guys I can wait :).
Take your time.
Robo
Soeren:
Hi,
--- Quote from: Robo73 on July 30, 2007, 04:02:27 PM --- a. How to connect the crystal to my chip ? It has two leads.
--- End quote ---
Like the datasheet shows of course. Between pins 7 and 8 and then a small cap (like 15..20pF) from each pin to gnd.
--- Quote from: Robo73 on July 30, 2007, 04:02:27 PM --- b. If I connect it will there be an interference between the external and internal clocks?
--- End quote ---
No. if it's driven from an x-tal, it isn't using the internal oscillator.
--- Quote from: Robo73 on July 30, 2007, 04:02:27 PM --- c. I've seen crystals that come in different shapes and numbers of leads. For example, I've seen one
that comes in a DIP chip. How would the connection be different?
--- End quote ---
Sounds like you're talking about x-tal oscillators, which is an oscillator with x-tal and buffer - for connecting it, consult the datasheet, you're expected to do a little of your own footwork.
--- Quote from: Robo73 on July 30, 2007, 04:02:27 PM ---If the ADC is used, it should be connected to VCC through a low-pass filter."
For the low-pass filter they're referring to, is is just a capacitor and resistor? what should their values be?
--- End quote ---
Why do you care? You claim you won't be using the A/D-C.
Soeren:
--- Quote from: Robo73 on August 03, 2007, 02:15:05 PM ---It's ok guys I can wait :).
Take your time.
--- End quote ---
You bloody well have to. This is people helping you in their spare time, so pipe down, we take our time without anybodys approval.
Want the right to such a rude post, then hire an engineering consultant - I'll charge you $225 an hour for consultancy work, so perhaps a more polite attitude is in its place?
Robo73:
Hello Soeren,
First of all thanks for the info you provided. Actually I'll be using A/D converter. That's why I said in my
original messege, and I quote:
" .... I just want to have one digital port, and 4 analog pins .... "
and also,
"PORTA is an analog port and I only need 4 pins."
So, if I want to use the analoge port (Port A) or actually some pins of it, then I must use the A/D converter.
Now, about the comment I made, it was suppposed to be a joke (i.e. for fun). That's why I put a smily face.
So, cheer up ;D.
Thnx again.
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