[time-nuts] Frequency Dividers

[SAIDJACK at aol.com]

In a message dated 8/8/2006 19:51:06 Pacific Daylight Time, didier at cox.net  
writes:
 
Hi Didier,
 
I used their 8051F310 in many devices, it's a great little chip :)
 
There are two issues that made me change to the Philips LPC2000 Arms  though: 
the SIL parts are somewhat expensive, and they don't have much memory,  
especially SRAM. For the Arm's, there are GNU compilers (no need to pay Keil),  and 
a bunch of great open-source RTOS'.
 
Also, the Arm's are extremely low-power, and run up to a true 60Mips at 32  
bits. Plus they have lot's of memory and code compression (Thumb mode).
 
Then there is Olimex and Sparkfun, they sell these Arms very cheap. Last  
time I checked, SIL wanted to have $99 for an 8051F310 eval kit - the Arm starts  
at $29.99 at Sparkfun - no need to buy any software development tools for the 
 Arm either.
 
Philips has parts with up to 512KB internal Flash and at least 64Kbytes  SRAM 
I believe, some of them pin-compatible to each other.
 
On the PLL: Philips typically does very well on their PLL's - jitter  is very 
low. Certainly I've seen some of their PLL's in the ps range, which  would 
put the 1PPS output at probably better than 1E-11, 1s accuracy. I can  measure 
the unit I have, and let you know later...
 
bye,
Said
 
 
 
 
 
 
 
 
 
 
 

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/Precis
ion_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.