Crystal Frequency ????

Brian Riley

I was just reading about a new Prop dev board someone had made and was considering offering for sale. One of the first things I noticed in the first pic I looked at was a 10 MHz crystal ... my mental comment was "I wonder why he picked that?" After some thought the only answer I could come up with was "I haven't the foggiest!"

Now the more I thought about it the more I realized that I really had no idea what the considerations were.

So, in my quest for enlightenment, I pose this question for the assembled multitudes ... "If I am going to design a Prop board. Why might I chose crystal/pll pair of 10 MHz/8x over 5Mhz/16x? What are my considerations? What are my tradeoffs?"

cheers ... BBR

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cheers ... brian riley, n1bq, underhill center, vermont
The Shoppe at Wulfden
www.wulfden.org/TheShoppe/

Oldbitcollector (Jeff)

Here's some reading to get you started.. [noparse]:)[/noparse]

propeller.wikispaces.com/Oscillator

OBC

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Leon

They are available in much smaller packages than a 5 MHz one. That's the reason why I'd use one.

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Leon Heller
Amateur radio callsign: G1HSM

Brian Riley

Interesting reading, learned a few new things, but it seems the only answer I got relative to my posed scenario of 5/16x vs 10/8x was Leon's comment about physical package size of a 10 MHz crystal vs a 5 MHz crystal ... since most of what I am working with involves the D40 package, that's hardly a concern for me ... now if I were working with something the size of the sexy little Prop Backpack, I can see it as a consideration.

Thanks for the info guys ... I am looking forward too seeing if anyone else has something to add.

cheers ... BBR

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cheers ... brian riley, n1bq, underhill center, vermont
The Shoppe at Wulfden
www.wulfden.org/TheShoppe/

mikediv

Brian if I understand what you are asking the reason for using a 10 meg crystal instead of a 5 or 6 meg is clock speed some of the guys drive there prop chips at 100 meg or higher , so with a 5 meg crystal you can only go 80 meg top speed.
so the higher the crystal speed the higher the speed of the prop chip itself I hope that helps.

Phil Pilgrim (PhiPi)

Brian,

Smaller physical size is the only reason for choosing 10 Mhz over 5 MHz, and then only if you're designing a surface-mount board. You will not be able to use a 10 MHz crystal with PLL16x to get 160 MHz.

-Phil

heater

Except I have yet to hear of anyone getting the Prop too run at 160MHz. Sapieha runs 120MHz a lot I believe.

I use 10Mhz XTALs just because I have a bucket load of them.

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For me, the past is not over yet.

hinv

I am hoping to tap into the 13MHz Crystal Clock oscillator of the Zipit, and run at 104MHz. Hopefully the thing will handle the extra load. Hopefully, I will be able to try it out tomorrow.

Cluso99

There is a school of thought that the internal PLL works better with a final /2. The actual prop internals always *16, so if you use *8 it will *16/2.

From overclock testing it seems higher xtals and *8 works better. Sapieha has 15MHz xtal on the TriBlade running 120MHz for nearly a year now.

My RamBlade works with a 14.31818MHz and *8, but 7.3...MHz *16 does not (14.6MHz). 15MHz *8 did not work. This has not been extensively tested though. Note 14.31818MHz is an NTSC frequency and is readily available.

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Links to other interesting threads:

· Home of the MultiBladeProps: TriBlade,·RamBlade,·SixBlade, website
· Single Board Computer:·3 Propeller ICs·and a·TriBladeProp board (ZiCog Z80 Emulator)
· Prop Tools under Development or Completed (Index)
· Emulators: CPUs Z80 etc; Micros Altair etc;· Terminals·VT100 etc; (Index) ZiCog (Z80) , MoCog (6809)·
· Prop OS: SphinxOS·, PropDos , PropCmd··· Search the Propeller forums·(uses advanced Google search)
My cruising website is: ·www.bluemagic.biz·· MultiBlade Props: www.cluso.bluemagic.biz

hinv

Have any idea why 13MHz would be common with the ARM? My Axim runs at 624MHz and the Zipit at 312MHz.
Maybe there's something I'm missing.

@Cluso, BTW, I was able to get my demoboard to run just fine at 14.31818MHz * 8, but not the 13.5*8. They both seemed to communicate just fine, but the 13.5MHz crystal just wouldn't do VGA. 14.31818Mhz on the same demoboard worked great.

Doug

Cluso99

hinv: Most likely you have some VGA parameters set incorrectly, or need changing. If the 14.31818 works then the 13.5 will work.

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Links to other interesting threads:

· Home of the MultiBladeProps: TriBlade,·RamBlade,·SixBlade, website
· Single Board Computer:·3 Propeller ICs·and a·TriBladeProp board (ZiCog Z80 Emulator)
· Prop Tools under Development or Completed (Index)
· Emulators: CPUs Z80 etc; Micros Altair etc;· Terminals·VT100 etc; (Index) ZiCog (Z80) , MoCog (6809)·
· Prop OS: SphinxOS·, PropDos , PropCmd··· Search the Propeller forums·(uses advanced Google search)
My cruising website is: ·www.bluemagic.biz·· MultiBlade Props: www.cluso.bluemagic.biz