AVR32 PLL Details - numeric limits on m/n

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The AVR data is sparse here, they give a formula, but no numeric ranges.

If I look at the register mapping, I infer that just 4 bits are used for M,N, but that hardly seems right ?
ie if your PLL goes to 240Mhz, then /16 stops at 15Mhz, missing a whole range of crystals.
Is there any hard info, on the numeric ranges that the PLL can actually work with ?

The whole idea of a PLL, is to allow more choices from a given crystal, and on a 32 bit chip, allocating very small numbers to PLL ranges, does not make sense.
We need to cover 3 target frequencies, and with good precision.

I see the LPC17xx has a useful PLL spreadsheet, that takes numbers, and reality-checks them - is there a AVR32 PLL-Calc equivalent ?

Hello,
the four bits are right. Atmel didn't implement the best PLL but for division you have the bits PM.CKSEL too. I don't know a PLL-calc tool but for that limited range you won't need it.

Thanks.
Bummer; looks like it's the LPC175x, which is a larger package, and more \$\$, than we otherwise need.

Does anyone know if any of the newer AVR32's have better PLLs ?

-sma

sma wrote:

Using the LPC175x PLL calculator, we can hit our 6 possible target frequencies, within 10ppm. (we should need only 3 in the final project)

Here, that's a VCO of 275-550MHz (post Div2), and then a XtalDiv of 5 bits (even tho the data suggests more) and a Freq Multiplier of 9 bits.

The RefFreq needed is from ~780KHZ to ~2-3MHz

So, only a slight improve from the very limited AVR32 design of 4 bits is needed : On the Xtal Div: 5 or 6 bits, and on the VCO Divider : ~9 bits. - and the PLL needs to cope with Ref Frequencies of >= 750KHz.

The LPC family can work down to below 32KHz Fref, and has some modes for 32.768 locking; nice features, but not needed on this design.

They also have a nice CLKOUT divider, that is separate from the CPU Divider, so we can get our targets on a pin, without imposing too many caveats on the core.

Hello,
if you want some help please ask some proper question or answer the right way to questions from the community.
What's mis understandable on

Quote:
?
You won't get an answer if you talk for a page about LPC175x but didn't tell us what's your need.

uC-Harry wrote:
Hello,
if you want some help please ask some proper question or answer the right way to questions from the community.
What's mis understandable on
Quote:
?

If you read carefully, you will see I gave an example of what I need.

uC-Harry wrote:

You won't get an answer if you talk for a page about LPC175x but didn't tell us what's your need.

The LPC is simply an example, and again, if you read carefully, this is what an _AVR32_ needs, in order to meet what we need :

["So, only a slight improve from the very limited _AVR32_ design of 4 bits is needed : On the Xtal Div: 5 or 6 bits, and on the VCO Divider : ~9 bits. - and the PLL needs to cope with Ref Frequencies of >= 750KHz."]

There, I have given actual bit-counts on the Xtal Div, the VCO div, and the RefFreq, which is as complete info as most need, to design a PLL.

What I asked above, still unanswered, was if any of the upcoming AVRs improved the shortcomings on the PLL ?

Hello,
sorry I didn't realize that you were talking about improvements of AVR32 PLL. We all know that the PLL could be better.
I thought you want some community support to find a good solution for your needs.