6.25 X-tal

BADHABIT

Rayman,

I was at your site a few days ago and saw a thing on there that said something like - using this and amultiplier of 16 you can run at 100mhz.
I have not returned to look it over again, but I figured that with all this recent talk about chrystals and allowed multipliers it would be helpful if this was elaborated.

Sapieha

Hi BADHABIT

It is posible to drive Propeller with crystals 14.318.180 and 15.000.000 MHz and PLLx8.
That give You more that 100MHz but it is Yours own risk.
Only problem with that You must have beter (in my case one 10uF tantalum on crystal side of Propeller) capasitors close to Propeller.

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Nothing is impossible, there are only different degrees of difficulty.
For every stupid question there is at least one intelligent answer.
Don't guess - ask instead.
If you don't ask you won't know.
If your gonna construct something, make it·as simple as·possible yet as versatile as posible.


Sapieha

Ale

As Sapieha pointed out you can use higher than 5 MHz crystals. But be aware that the propeller can be reliably used: in the whole temperature range and voltage range up to 80 MHz.
But IF you keep it in a cool environment and with stable 3.3V you can use it till 110 to 120 MHz. Beyond that has been proven to be problematic due to the inherent process used, etc.
I'd use a 7.1 MHz crystal instead of a 14.3 so the PLL will not be so over the limit (it will multiply by 16 anyways). 6 MHz is quite reliable (96 MHz) and most VGA drivers work for example. 6.25 MHz gives you 10 ns per clock but those crystals are not that easy to find. 6.5 MHz crystals are quite common and give you 104 MHz. The 7.1 MHz crystal (2 times the chroma carrier) will give 114.56 MHz but as Sapieha said improve your decoupling. The DIP package has only 2 VDD/VSS pins but the QFP and QFN have 4, I'd use some 1uF/100nF/10nF capacitors in parallel for each pin.
There are a couple of thread about this same topic already. be sure to search using search.parallax.com

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Visit the home of pPropQL, pPropQL020 and OMU for the pPropQL/020 at omnibus.uni-freiburg.de/~rp92

Sapieha

Hi Ale.

You said "I'd use a 7.1 MHz crystal instead of a 14.3 so the PLL will not be so over the limit (it will multiply by 16 anyways)."
It is not true. But I can't explain it for You without permission from Chip.
Any way it function beter with 14MHz not 7MHz (More stable)
With 15MHz I run ViewPort without any problem in communication betwen Propeller and ViewPort

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Nothing is impossible, there are only different degrees of difficulty.
For every stupid question there is at least one intelligent answer.
Don't guess - ask instead.
If you don't ask you won't know.
If your gonna construct something, make it·as simple as·possible yet as versatile as posible.


Sapieha

hinv

I just tried out 2 different 8MHz crystals that I was able to salvage from a dead laptop. They worked fine for some blinky LEDS, but I have yet to try them on programs with TV or VGA output yet. As the counters are the first to go, it might not work.

Ale

As a scientist I cannot accept you word for it. I'd need some evidence. If you are using a 14.3 MHz crystal and the PLLx8 tap you should get the same result as if you use a 7.156 MHz crystal and a PLLx16 tap unless there is something that is described in the datasheet that is different in reality. Well, I'll wait and see what others have to say.

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Visit the home of pPropQL, pPropQL020 and OMU for the pPropQL/020 at omnibus.uni-freiburg.de/~rp92

Leon

8 Mhz is the max. crystal frequency when using the PLL, according to the data sheet. It obviously works when using a higher frequency, but I wouldn't do that for anything that was going into production.

Leon

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Amateur radio callsign: G1HSM
Suzuki SV1000S motorcycle

Post Edited (Leon) : 5/31/2009 9:53:49 AM GMT

Sapieha

Hi Ale.

In reality PLLx16 is not an divider at al. divider stages is only PLLx2, 4, and 8.
PLL always multiply crystal frequency by x16.
That give You with PLLx16 unbuffered frequency to Propeller logic.
If You are a scientist You must know that PLL can't give You stable square wave without special bufering.
But if You use divider that can act as buffer and conditioner, You have very stable square wave on its output to Propeller logic.
And it is very important with high frequency ratios.

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Nothing is impossible, there are only different degrees of difficulty.
For every stupid question there is at least one intelligent answer.
Don't guess - ask instead.
If you don't ask you won't know.
If your gonna construct something, make it·as simple as·possible yet as versatile as posible.


Sapieha

Post Edited (Sapieha) : 5/31/2009 9:54:53 AM GMT

Ale

You did not understand my use of the word scientist at all :-(. It does not relate to amount of knowledge it relates to the way of acquiring it and verifying it to be accurate between some boundaries, among other things.
The small piece about: there is no buffering between the x16 tap the the clocked circuits was missing. The rest (as I said) was known. Ok, thanks.
228 MHz is well beyond the maximum 160 MHz of PLL output frequency. As some experiments showed your are quite in the limit zone (and with 15 MHz more so). Maybe they can extend the recommended range to 96 .

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Visit the home of pPropQL, pPropQL020 and OMU for the pPropQL/020 at omnibus.uni-freiburg.de/~rp92

Rayman

Prop runs fine with 6.25 MHz crystal and PLL 16X for 100Hz, giving an even 10-ns between clock ticks. The end of the new datasheet actually shows the working frequency range with respect to temperature...

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My Prop Info&Apps: ·http://www.rayslogic.com/propeller/propeller.htm

BADHABIT

So even higher operating speeds could be acheived if a peltier cooler was used and the multiplier was regulated by a temperature controlled variable

From the datasheet it looks like you could roll @ 100 all day long

Cluso99

BADHABIT says "looks like you could roll @ 100 all day long".
That's my take on it as well. However there is a PLL failure issue with the prop and I don't know if this will exagerate the problem.
FWIW 12.5MHz xtals are easier to source than 6.25MHz.

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Bill Henning

I think you guys will like my announcement:

http://forums.parallax.com/forums/default.aspx?f=25&m=355996

I could not sit here reading this thread any longer without letting you guys know that 6.25MHz crystals are no longer scarcer than hen's teeth!

Bill

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