AT91SAM7S oscillator?

I'm trying to figure out how the oscillator is working in the AT91SAM7S from Atmel. The data sheet lists that an up to 20 Mhz crystal can be connected and the summary says that the oscillator runs at up to 55 MHz - is the crystal frequency multiplied by 2.75 or what?

The system I'm developing needs a 6.0MHz and a 5.12MHz oscillator - will it be configure the PCK0-2 outputs to these frequencies while running the controller at near maximum speed? I have read the data sheet of the AT91SAM7S but I'll need some help on this, which is highly appreciated.

Thanks, orc

Reply to
orc
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It might be a good idea to read the section of the processor's specification entitled "Clock Generator". Look at the description of PLL.

Reply to
Grzegorz Mazur

Thanks. Yes, that's the section i read (twice actually :-) ) but still having several qustions to it - the most important is the one I mentioned: is it possible to have a 6.0MHz and a 5.12MHz oscillator output to other devices like an external ADC'es etc. while running the processor at a speed near it's max (55 MHz)? (I do not need to know how yet, because I'm only designing the hardware and need to pass the design to our PCB-layouter for layout very soon - just need to know if it is possible at all or if I need to have additional X-oscillators for the ADC's etc.).

As far as i understand the crystal is the input to the Main Oscillator which runs at the same frequency as the crystal. The Main oscillator frequency can be divided by a factor 1 to 255 and the output from the divider goes to a multiplier in the PLL that can be set to a factor 1 to 2047 which determines the PLL frequency. The data sheet lists that the input frequency to the PLL must be between 1 MHz and 32 MHz and that the output frequency must be between 80 MHz and 220 MHz - how is that possible - this means that the multiplier can only be used in the range 3 (3 * 26.7 MHz = 80 Mhz) to 220 (220 * 1 MHz = 220 MHz) and not 1 to 2047 ???? This is just an example of my confusion.

Thank you for your help.

Best regards, orc

Reply to
orc

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