Pls How can I make 16F877A use 15MHz Xtal

[T.Jackson]

Hi I am using a PIC 16F877A in my project. The Project works fine with a 4MHz crystal but when I replace the 4MHz crystal and its associated capacitors with a 15 MHz crystal and associated capacitors, The pic does not work
Does anyone know what needs to be done in PIC basic to make the 16F877A work?
Thanks

There is actually a variant of the 877a that is limited to 4MHz. 877a-20p will work up to 20MHz

[ozzie1st]

T.Jackson,
Yes not to mislead anyone; I typed 15 loosely here. It could have been 8, 16 20 etc; I simply couldnt get any crystal (8, 20, 16 etct) to work. OF course PBP will not compile with DEFINE OSC 15. But it did compile with the listed frequecies 16MHz, 24MHz etc. However at the time I entered this thread I did not know that PBP wil not work with 15
However Thanks to the forum I now know better and I am actually using a 24MHz crystal;-)

[paul borgmeier]

Hi Ozzie,

Now that everything is fine, it is not. This time you need to check the datasheet. You will see that 24MHz is beyond the specified limit of DC-20MHz. You are "overclocking" the PIC and performance is not implied.


Hi Alain, you quoted skimask's reply from post#4 and then wrote this

geeeee !!! What a wonderful forum is has become these days ...

after all these years, I didn't know there was a DEFINE OSC 15 ...

12 or 16 only available ... too bad !!! ( Manual p. 170 ... )

for clarification, skimask did not suggest using DEFINE OSC 15, the OP did (post#3). Skimask hinted that the OP might want to check the manual (post#4).

in otherwords, skimask asked him to fish (post#4), I baited the hook (post#5), and you gave him a fish (post#13).

EDIT: and I had a little fun with the m M thing along the way (Trent also noted the 20MHz top limit above)

[T.Jackson]

T.Jackson,
Yes not to mislead anyone; I typed 15 loosely here. It could have been 8, 16 20 etc; I simply couldnt get any crystal (8, 20, 16 etct) to work. OF course PBP will not compile with DEFINE OSC 15. But it did compile with the listed frequecies 16MHz, 24MHz etc. However at the time I entered this thread I did not know that PBP wil not work with 15
However Thanks to the forum I now know better and I am actually using a 24MHz crystal;-)

I'm unaware of any variant of the 877a that can be clocked as high as 24MHz.

[skimask]

I'm unaware of any variant of the 877a that can be clocked as high as 24MHz.

Maybe I'll send you my special one that was clocked at 32Mhz for awhile.
I don't know why it worked, but it did. Would it work under all conditions, using all modules, under all combinations of code? Probably not, but it worked for me.
(Yes, I know it's a one-off situation and they're only rated for 20Mhz)

[Acetronics2]

Hi, Skimask

ALL the pics I use are "overclocked" to their max. "µChip" freq. ... my old 16F84-04, 16F628-04, 16F876-04, 16F877-04 and else happily run @ 20 mhz.
32 Mhz is not really surprising nor, I often read about !!!

this fact is well known, also well known those chips have not being TESTED over the whole voltage, temp. and freq. range !!!

Just keep in mind those overclocked chips are not guaranteed by µChip ... that's the only point to care with when professionnal use !!!

May be we also might point out that , these days, "Non Rohs" devices are sold at a really fair price ...

Alain

[T.Jackson]

Maybe I'll send you my special one that was clocked at 32Mhz for awhile.
I don't know why it worked, but it did. Would it work under all conditions, using all modules, under all combinations of code? Probably not, but it worked for me.
(Yes, I know it's a one-off situation and they're only rated for 20Mhz)

Nah I'll be right. Not in the habit of challenging large teams of professional engineers. The data sheet says 20 - that's as far as I go.