Timer1 frequency counter limit

ERICOO · Joined: 13 Jun 2011 Posts: 14 Location: NIGERIA

I have learned PIC MCU programing to the level that want to make a digital read out from my analog tuner world receiver. I will pick the signal from the mixer stage and input onto a frequency counter. But i need to be cleared in these two areas.

1) is it possible for the 16F8XX family of mcu to measure frequency above 20 MHZ when the specified max freq. response is 20 MHZ?

2) can the CCP1 module which is a 16 bit register with max. 8 prescaler measure up to 100 MHz ?

Needs your views thanks

Eddy71ua · Joined: 23 Sep 2009 Posts: 55 Location: Ukraine

I tested Timer1 module, it work correctly up to 70MHz.

Ttelmah · Joined: 11 Mar 2010 Posts: 19333

What individual examples will do, will be much better than the specified figures (which should be achievable by all chips, right across their operating voltage specs). The frequency limit for the CCP counter, is not '20MHz'. It is specified in the data sheet as an input period >:

(3Tcy+40)/N

where N is the prescaler used.
So with /16, and a chip at 20MHz (Tcy=50nSec), equals

(150+40)/16nSec = 11.875nSec, or 84MHz.

However there are also limits for the high time, and low time, at 20nSec each, with the prescaler, so 25MHz is the highest 'warranted'. Individual chips, at particular voltages, may well go far past this.

However realistically, why not just use an external hardware /10 divider?.....

Best Wishes