View Full Version : SX Key to clock Prop?

User Name
11-08-2010, 09:23 PM
One of the many things that made the SX Key so outstanding was its ability to synthesize most any frequency. (BTW, does anyone know what its granularity was? I know the software will accept any arbitrarily value that is within its operating range, but there is evidence that it doesn't actually generate any arbitrary value - rather it defaults to the nearest frequency it can deliver.)

I wonder if an SX-Key could be used to clock a Propeller? The 5V vs 3.3V isn't the issue. I guess the question is: What would be the simplest way to trick the SX Key into configuring and running its generator? Could the Prop itself do that?

I guess it could be done by using an actual SX chip and running the clock line to the Prop. I wonder if that's the only practical way?

Phil Pilgrim (PhiPi)
11-08-2010, 10:07 PM
The clock from the SX Key was not produced by its own SX but by a clock synythesizer chip (in my SX Key, an ICD2053, which has been discontinued). There's no reason a similar chip could not be configured by the Prop in fast RC mode on powerup, then used to clock the Prop itself.


Martin Hodge
11-09-2010, 05:11 PM
The USB key uses an ICS307 to generate clocks.

User Name
11-09-2010, 06:22 PM
Thank you, sirs! Ever since Phil's post, I've been wading through the plethora of synthesizer chips made by Cypress, TI, and others, and was favorably considering the TI CDCE913. But the ICS307 looks like a great choice, too. Its datasheet is certainly more friendly and well-organized, and its interface seems simpler.

Anyway, I like the direction this is taking. There are still some details to be worked out about making the transition from internal RC timing to external clock. It may even be that I provide a mux to select between two external sources - one fixed and one programmable - just so that the Prop can vary the programmable source on the fly w/o messing up the timing of the serial communications that are effecting that change. On the other hand, I2C slaves are fairly tolerant of timing variations. We'll see. :)

Phil Pilgrim (PhiPi)
11-09-2010, 06:27 PM
Neither SPI nor I2C should have trouble at RCFAST speeds, so I doubt that you'd need to consider a gatable external clock source.