Internal RC external crystall

Go To Last Post
8 posts / 0 new
Author
Message
#1
  • 1
  • 2
  • 3
  • 4
  • 5
Total votes: 0

Hi

On the weekend I built the DotMatrix clock from the Academy.

The circuit uses the internal RC set to 1Mhz and an external 32,768kHz crystal.

The question is how does this work.
How could the developer of this circuit be sure that the signals dont get mixed up.

You can also see the circuit here:
http://tobiscorner.shellmaster.d...

Cheers
Rubi

  • 1
  • 2
  • 3
  • 4
  • 5
Total votes: 0

While im not 100%sure (didnt follow link)

My guess is that the 1Mhz RC controls(clocks) the Code and the 32Khz, makes a 1 sec interrupt for the Watch.

The AVR has 2 special clock pins for the 32Khz

/Bingo

  • 1
  • 2
  • 3
  • 4
  • 5
Total votes: 0

The signals are totally seperate. The 1mhz internal RC is only important to the AVR chip in the first place, the external clock crystal is simply the input for an internal asyncronous timer, and should not cause a problem as long as the crystal is close to the AVR. Tt has internal driving circutry to use the crystal. There's really no way for you to 'mix up' anything.

-Curiosity may have killed the cat
-But that's why they have nine lives

  • 1
  • 2
  • 3
  • 4
  • 5
Total votes: 0

Hi there.
This is exactly what I'm doing now. I use the ATMega16, with internal RC 4MHz and a 32,768KHz external crystal mount to the TOSC pins to trigger the 8bit Timer2. A timer2 overflow interrupt occurs every 7,8ms and I update my real time clock.
You know something? It works fine.
--------------------------------------------------------------------------------------------------------
Michael

Michael.

User of:
IAR Embedded Workbench C/C++ Compiler
Altium Designer

  • 1
  • 2
  • 3
  • 4
  • 5
Total votes: 0

Hi All

Thanks for the answers.
It works also fine on my clock.

But I was really impressed , how the ATMega 8 could differentiate the "two" oscillators.
Since the crystall was mounted on XTAL1 and XTAL2 .

On the Mega16 with internal RTC I wouldn't wonder about such configerations,...

Cheers
Rubi

  • 1
  • 2
  • 3
  • 4
  • 5
Total votes: 0

Rubi wrote:
Hi All

Thanks for the answers.
It works also fine on my clock.

But I was really impressed , how the ATMega 8 could differentiate the "two" oscillators.
Since the crystall was mounted on XTAL1 and XTAL2 .

On the Mega16 with internal RTC I wouldn't wonder about such configerations,...

Cheers
Rubi

What internal RTC ??
I missed it if there is an internal RTC in the M16 :?:

/Bingo

  • 1
  • 2
  • 3
  • 4
  • 5
Total votes: 0

I think he's referring to the Mega16's independent RTC pins TOSC1 and TOSC2, as opposed to the pins shared with XTAL1 and XTAL2 on other ATMega devices.

  • 1
  • 2
  • 3
  • 4
  • 5
Total votes: 0

Dear mneary

Thanks for correcting me.
That was exactly what I meant.

Cheers
Rubi