Printable View
I hate to run a PIC off specs,
so do I hate having to ask this,
but. . .
does anyone have any experience with running a PIC at clockspeeds higher than specified in the datasheet?
The reason I'm asking is:
on one of my projects I have got to run the PIC (16F628) at 8 MHz
I can get the 4MHz versions at about half the price of the 20MHz versions.
If the PCB was designed for the DIP Version, and the PICs were easy to replace
I would just give it a try, but with SOIC... ?
Regards
Ralph
Hi, nav
I did a small try ... with a PIC 16F628/04
It works fine at ...20 Mhz !!! and it works with a lot of PULSIN, RCTime and Pulsout ...
Seems 4 Mhz are 20 Mhz pieces out of µChip speed spec's ...
doesn't cost anything to try !!!
Alain
For sure it can work... at ambient temperature! I'm not going to hope that it will always start/work properly for awhile/forever in all condition. Can work with some crystal but not with others and such other...
For sure you can use almost every electronic parts a bit over their spec and it will work... how long? that's another question. If you don't give any warranty/support and you're not afraid to burn your name, now you can do it for sure... That's my own opinion on that.
what is the main need of 8MHZ oscillator? Serial comm? in this case why not using lower baudrate (2400,4800)?
i don't know where you get your parts but 20MHZ is not twice the price of a regular 4MHZ... see digikey u.k website.
Hi, misty ( sorry ... Mr E !!! ) and welcome.
Here, I got my 16F628/20 to Conrad's at a bit less than 5 Euros per 10 ... with the 20% Christmas savings !!!
16 F628/04 are much more expensive ... in France.
available at 4.5 Euros in Brussels ... at Mbtronics.com and overall ... They also sell the wonderful and unfindable Picstart plus Upgrade - at a very reasonnable price -
see their very interesting ( refs AND prices ) page ... and note they are very serious guys !!!
Yesssss, I know ... Conrad and MB are for Europe !!!
Ah, last thing, how do you think low price electronic components are possible ???
Simple: you buy a lot without been tested or out of specs ( no garantee from the manufacturer ), and you assume the garantee, hoping the manufacturer is serious ...
so, you get 99.9% good and maybe .1% to keep aside ... good to try for Hobbyists, no ???
I know a lot of pro people doing that for computer components and peripherals ... test is done at their factory.
Might be it creates good benefits !!!
Alain
There are several reasons for asking this:
50% of the Boards have already been manufactured and and have a 4MHz chip on board.
Attaching a 8 MHz Resonator (Pads are there) is a lot easier than replacing the PIC.
I have got a "special offer" for the 4 MHz SMD version,
it is really half the price of the 20MHz version.
The higher clock speed is a must for capturing synchronus serial data on this project.
(reducing comms speed is not an option)
The board I'm using on this project was initially designed for a different project where 4MHz was sufficient.
In the meantime I have done some testing
and it turned out that the 4MHz chips run reliable up to 12 MHz,
in a temp range of 0 - 50 deg C.
(I haven't tested any higher clock speed or temperatures)
As I'm planning to run the PIC at 8MHz
in a temp range of 25 (+-10) deg C "only" I think its worth giving it a try.
I totally agree,
it would be better to run all components within the specs, but this time I do not really have a choice as cost is THE key issue.
P.S.
I dont know how PICS are tested at MicroChip,
but lets assume there is no separate production for 4MHz Chips,
it is just a question of did the chip pass the 20MHz test.
case yes stamp 20MHz onto the chip
case no stamp 4MHz onto the chip
If this assumption is correct
I will be running a chip that was designed for 20Mhz but did not pass the test
at "only" 40% of the speed it was initially designed for.
regards
Ralph
that's for sureQuote:
As I'm planning to run the PIC at 8MHz
in a temp range of 25 (+-10) deg C "only" I think its worth giving it a try.
Yep it's my assumption too or worst... ther'e the same only the stamp is different... i hope everything will work for awhile.Quote:
I dont know how PICS are tested at MicroChip,
but lets assume there is no separate production for 4MHz Chips,
it is just a question of did the chip pass the 20MHz test.
If this assumption is correct
I will be running a chip that was designed for 20Mhz but did not pass the test
at "only" 40% of the speed it was initially designed for.
BTW keep us post on it.