[time-nuts] Frequency Dividers

[Didier Juges]

I have used a number of pll controlled microcontrollers, and I would not 
recommend using one of those in a timing application such as those 
discussed here.

These PLLs are generally not very clean spectrally (it's actually a good 
thing for EMI, some chips have purposeful spread spectrum clocks) and 
may have lots of jitter.

However, most of the chips with PLL will let you disable the PLL and run 
from a crystal or an external oscillator. Alternately, it you use the 
timer instead of software loops, you can run the core from the PLL as 
long as the timer itself is not driven from the PLL.

I use the Silabs C8051F133  in several projects and it will run with up 
to a 100 MHz clock (with many instructions running in one clock cycle) 
from the PLL or I believe 50 MHz with an external oscillator. And if you 
needed a 16 x 16 MAC engine for that counter, it has that too :-)

http://www.silabs.com/public/documents/tpub_doc/dsheet/Microcontrollers/Precision_Mixed-Signal/en/C8051F12x-13x.pdf

That's not your father's 8051!!!

For timing applications, it has 5 general purpose 16 bit timers and a 6 
channel 16 bit Programmable Counter Array, so by using one of the 16 bit 
timer as a prescaler for the PCA, you can have create up to 10 
low-jitter timer outputs with 6 of them having up to 32 bits capacity, 
with minimum software overhead, so the CPU is mostly available for 
anything else you might want to do with it..

Pretty neat, uh?

The other day, a rep for a well known semiconductor/microcontroller 
company that shall remain nameless was showing me their latest ad for an 
8051 running at 50 MHz with a 4 clock core and in big letters: FASTEST 
8051 AVAILABLE. I pointed him to the Silabs web site and left him there...

Didier KO4BB

PS: only problem for the hobbyist, it only comes in a surface mount 64 
or 100 pins TQFP (cheap development boards are available, with JTAG 
programmer, prototyping area and serial interface). I am not associated 
with Silabs, however I am a very satisfied customer and I can recommend 
their products (hardware and software), they are topnotch and Silabs 
customer service is excellent. I routinely use them in products that 
operate way outside the generous -40 to +85 C temperature range without 
any problem.

SAIDJACK at aol.com wrote:
>  
> In a message dated 8/8/2006 14:29:38 Pacific Daylight Time,  
> Randy at synergy-gps.com writes:
>  
> Hi Randy,
>  
> the Micro's allow you to do other stuff, like discipline the OCXO as well  :)
>  
> BTW: I took a closer look at the Sparkfun board, the chip has a bunch more  
> Match outputs than I thought.
>  
> The Philips parts have great counters/PWM units (driven by an internal PLL)  
> for experiments.. The MSP430 should do the trick as well.
>  
> bye,
> Said
>
> Said,
>
> Thanks for the clue on the Philips part. Sounds like a  nice solution.
>
> I just got a couple of sample parts from Maxim that I am  going to play
> with (DS4000, MAX5121, and MAX6629). If they can do what  Maxim claims it
> might be a fun experiment. I have one of those little TI  MSP430 dev kits
> that I am going to try to use to run the show. We'll  see.
>
> Randy
>
>
>
>
>
> _______________________________________________
> time-nuts mailing list
> time-nuts at febo.com
> https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
>
>