Why would a 4MHz rated PIC not run at 20MHz?

[Sputnik]

The only PICs I am able to buy are rated at 4MHz. But the construction between the 4MHz and 20MHz PIC verisions aren't different are they? So why would a 4MHz rated PIC not run at 20MHz? Must the HS oscillator option be used instead of the XT option?

Sputnik :idea:

 

[FoxyRick]

Re: 4MHz PIC

PIC's can certainly be overclocked. Microchip (like many others) may only make one version of a chip (for financial reasons) but sell it marked at different speeds. Other manufacturers may make only one version, but test them to see which will work at the higher speeds.

See this thread for enlightenment:



Cheers,
FoxyRick.

 

[nooknikz]

4MHz PIC

A new version of PIC can run over 4 MHz
such as :
16F877A-I ( 4 - 20 Hhz )
16F877-20 ( 4-20 Hhz )

 

[olemp]

Re: 4MHz PIC

So why would a 4MHz rated PIC not run at 20MHz? Must the HS oscillator option be used instead of the XT option?

Sputnik :idea:

i have used 4MHz PICs(16f84 and 16f877) in 10 Mhz and 20MHz without any problem.
as oscillator fuse i have used xt or hs and could't see any difference....
bu it's better to use hs option according to data sheets...

 

[metal]

Re: 4MHz PIC

Hello

I have PIC16F84A-4 I/P, I want to use 20MHz crystal, shall I use HS fuse rather than XT, or there is no difference regarding the seection of HS or XT fuses.

Thanks in advance

 

[zapotec]

Re: 4MHz PIC

4MHz or 20MHz are factory selection for same chip.
Can be that a 4MHz classified chip run on highter frequency, but this is not sure for all voltage / temperature range.
You can set HS fuse in every case.
Regards
Zapo