Keeping two SX28's in sync?

cbmeeks

I have a project that I would like to use two SX28's. I would prefer to run them off one clock if I could.

Is that possible/practical?

What kind of problems will I run into keeping them in sync?

Thanks

cbmeeks

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Paul Baker

You will need to use a TTL oscillator or other active oscillator in order to do that, you should also try to keep the distance between the oscillator and the SXs equal in length to match the parasitics and skew of the clock, finally you should try to keep all other routing away from these lines to prevent coupling/crosstalk.

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1+1=10

Clock Loop

You can slave one with the other. Using serial out. Yea you could put them on the same clock, but that seems like alot of work.

Heres what I did.

I Used serin, and Serout.

When I wanted my slave device to WORK, i sent it serial data.

If I didn't send my slave serial data, it would sit in serin, waiting on data. (if you don't use timeouts.)

You could just send a sequence of numbers, 1 thru 255, and repeat. Or something.

Using this way, you could also synch your slave up to your master, by the data sent over.

You could also put them on the same clock too. Of coarse it really depends on what your end goal is.

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Meh. Nothing here, move along.

Paul Baker

Peter (pjv) has a really cool software method of syncing, Id search for it but I packing for a trip at the moment.

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1+1=10

Benjamin_baker

What's the application?

pjv

Hi cbmeeks;

It's a little tricky, and quite hard to explain, but I have been able to keep around 65 (thats all I needed; there is no practical limit) SX's running continuously in sync for almost ten years now. Each uses its own (50 MHz) resonator, and each will lock onto the selected "master" to one instruction; 20 nSec. If lock is lost on one, say a power down on it, it will regain a lock typically in 100 uSec.

In order to achieve these results you need to be VERY precise in how you write your software in the ISR routine. Although in concept it's very simple, it's not suitable for the "casual" programmer, and tools such as a GOOD oscilloscope is pretty much a neccessity. And yet, once the syncing method is established, almost any other application software can be merged in with it, including my 8 thread pre-emptive realtime operating system. I principally use it with Virtual Peripherals such as ADCs, DACs, UARTs, digital inputs, relay outputs, etc. for industrial monitoring and control.

Cheers,

Peter (pjv)