6.25mhz crystal oscillator

Franny

What's the purpose of having the ability of swapping crystals?

Bill Henning

So you can run at 100MHz giving you 10ns timing resolution and 25MIPS per cog

Franny

But what's the point? How is it different from the 5mhz?

Martin_H

Running the Propeller at 100 mHz instead of 80. So you get more cpu cycles. It's basically over clocking.

Franny

Oh, I see, So what's the catch when you overclock it, Can it crash?

jmg

Franny wrote: »

Oh, I see, So what's the catch when you overclock it, Can it crash?

You have less margin, but remember the 80Mhz is at high temperature and low voltage.

Many vendors specify more than one Frequency, and the Prop probably should do that too.
Currently they have a single spec of this
ie -55°C < Ta < +125°C, >2.7V => Up to 80MHz,

They could probably add something like
ie -40°C < Ta < +85°C, >3.0V => Up to 100MHz

Franny

Thanks for the help.

Duane Degn

The Parallax Laser Range Finder uses a 6MHz crystal and runs at 96MHz. Apparently the extra speed was required to interface with the camera used on the LRF.

As you've probably noticed, a lot of Propeller boards use a socketed crystal. I'm sure there are special sockets for this purpose but you can also use these machine headers as crystal sockets.

blittled

The PropScope uses a 6.25MHz crystal so it can do 100MHz A/D sampling

Cluso99

I regularly overclock the prop to 104MHz using a 6.5MHz xtal. But be warned, overclocking also requires special layout and use of decoupling capacitors. There are a number of threads that address these issues.