What is a prescaler?

[Sachin]

I have the term "prescaler" used a lot. What exactly is it and where
can I get more information (tutorial-like)?

Thanks,

sachin

[William L. Bahn]

A prescaler is nothing more than a scaling operation that occurs before the
primary operation.

For instance, if you have a clock running at 64MHz and you want an output
clock running at 1MHz, you can bring the clock into a circuit and then use
the circuit to divide it down by a factor of 64. Or, you can use a
divide-by-16 circuit on the clock itself and clock the entire circuit at
4MHz and now the circuit only has to divide by 4. The divide-by-16 circuit
acting on the clock is a prescaler.

The advantage of a prescaler like this is that you can implement it easily
in hardware which makes the software cleaner and tighter and you can get
significant power savings by having the bulk of the circuitry clocked at a
lower frequency.

Prescalers do not have to be clock dividers (though that is the most common
context with which I am familiar although prescalers that multiply and/or
divide values by powers of two by shifting bits left or right are fairly
common as well) or even digital in nature - although when they are used in
the analog world they are more commonly called preamplifiers.

Sachin wrote in message <9b3f034e.01071...@posting.google.com>...

[Skipp]

I like the other guys text so I'll just add something different on my own.
One will often see prescaler hardware used around the front of a frequency
counter to "extend the counters usable range."

An example would be an older TTL Chip frequency counter that counts to
30MHz on a good day, with a tail wind... :-) A divided by 10 prescaler
box placed on the input of the counter would take a sine wave up to 300MHz
and divide it down (by 10) to input into the counter. Plessy is/was a
large mfgr of prescaler chips and the 11C90 is a generic number for a
typical chip made by many.

Ramsey makes some lower cost frequency counters with prescale front ends.
The basic internal chip set by itself might be good to say 60MHz, then a
front panel switch for the higher/second range places an internal mounted
prescaler chip in front of the "basic counter" section and you get
operation up to 600MHz. It's a common thing to find in many older
frequency counters.

Ramsey probably still sells an external counter prescaler kit/box.

cheers
sk...@pilot.ucdavis.edu
http://sonic.ucdavis.edu lot's of amateur radio electronics goodies.

: Sachin <sg...@my-deja.com> wrote:
: I have the term "prescaler" used a lot. What exactly is it and where

[Robert Bolam]

In the case of Microcontrollers which have an internal timer whether it
be for counting or a watchdog then the timer may have a programmable
binary divider to extend the timers period, this divider is known as a
prescaler.

I tend to use the PIC series of Microcontrollers, full details of the
prescaller's can be found on their websites.

Bob