16F876 : settings for 40Mhz

[mischl]

hello

would somebody be so nice to tell me step by step what are the settings for 40mhz operation? i'm work with a 10 mhz resonator and searched at the net for the right information... where can i find such depth informations by myself?

thanks a lot

[Melanie]

You're out of luck, there is no 40MHz setting for this part.

As far as I am aware, the 16F876 only goes to 20MHz (and then you need a 20MHz xtal).

Some 18F parts have an internal x4 PLL which will allow you to run at 40MHz with a 10MHz xtal, but the 16F876 does not have that feature.

Always check the PIC's Datasheet which you can download from the Microchip website.

[Acetronics2]

Hi, Mel

This thread points off a basic question ...
Do someone hereby have any experience about PIC ( real ...) overclocking ???

Results, maybe, could be interesting ...

Alain

[NavMicroSystems]

Alain,

I have 4MHz chips running absolutely stable @ 8MHz,
but I have never tried to overclock a 20MHz chip.

[Acetronics2]

Hi, Ralph

Yesss, I remember we already had a discussion about "4 Mhz" stamped chips ... that are , in fact, not verified 20 Mhz chips.

Just as my Pentium III 1200 runs quietly at 1287 Mhz ...

here the question is really : What happends at more than 20 Mhz for 20 Mhz max. chips ??? ... and also what happends to 18 F series if XTAL is more than 10 Mhz ...
Correct timing will be the next step ...

My toaster becomes old ... I hope hot plastic smelling not too awful ...

Alain

[Melanie]

If it's for your own project, go try it. If it works, then fine. If it dies, then no harms done (unless it's your own personal Pacemaker you're modifying!). I'm kinda boring - I almost never build things to exceed manufacturers component specs - it's a sure road to disaster.

If it's a marketable product for sale, DON'T. It's bad practice to run at (or beyond) maximum ratings (apart from the fact that you'll almost certainly invalidate your Public Liability Insurance!).

If you buy a car sold as capable of 160mph, then you would like to know that it'll do that all day long regardless of ambient conditions. Would you be happy knowing that when you reach 160mph it's within 0.1% of blowing it's head (or worse)?

Kiddies (and techies who should know better) like to tinker and overclock their PC's for example... then halfway through a major piece of work it has a cardiac and they end up crying into their coffee about the f****** PC and how much work they've lost. Go down this road and it's your own fault if things go wrong or you end up wasting heaps of time chasing your own tail. I'm not saying it doesn't work, but I am saying you are skating on thin ice.

Just as my Pentium III 1200 runs quietly at 1287 Mhz ...

Hmmm... a 4MHz PIC running at 8MHz could be compared to your P3-1200 runing at 2400MHz... might have some reliability issues here...

[Acetronics2]

HI, Mel, you're a real Mother for me, ( note here I'm very young today ( no peacemaker rqd )... Yeaaahhh , frenchies .... !!!)

Seriously, that kind of game ( really a game !!! ) is not to be used on security devices, nor sold !!!
My last car was a Honda civic 130 HP ... and ran only once at 180 Km/h intead of 201 . I was late for the first inspection !!! never went over 140 for the 14 following Years.
I now do recommend you the European Accord ... really, really great. - and wonderful if talking electronics ...

Back to Pics, remember those kind of treatments are only for my lab experiments, I perfectly know about components lifetime ... and use them aboard MY model planes ...

And never drink coffee nor else around my computer ...I assembled it myself, and don't want to crash or destroy it Stupidly.

Best regards
Alain

PS : for computer overclocking ... we won't discuss upon Windows tremendous qualities ... Why do I still run W98 SE ??? ....

[mischl]

ok, i now have a 18f242 with the possibilty to clock with 40mhz. and i have read the manual with the pll section. now i know that i must configure something the FOSC bit to multiple with 4. how i do that exactly in PBPro or with a assembly line inside?

thanks a lot for an explanation. greetings from a geek

[mister_e]

you must se configuration fuse and add a DEFINE OSC 40 at the top of your code

look here to know how to define your config fuses

the end of your 18f242.inc file look like this

;Configuration Byte 1H Options
_OSCS_ON_1H        EQU  H'DF'	; Oscillator Switch enable
_OSCS_OFF_1H       EQU  H'FF'
_LP_OSC_1H         EQU  H'F8'	; Oscillator type
_XT_OSC_1H         EQU  H'F9'
_HS_OSC_1H         EQU  H'FA'
_RC_OSC_1H         EQU  H'FB'
_EC_OSC_1H         EQU  H'FC'	; External Clock w/OSC2 output divide by 4
_ECIO_OSC_1H       EQU  H'FD'	; w/OSC2 as an IO pin (RA6)
_HSPLL_OSC_1H      EQU  H'FE'	; HS PLL
_RCIO_OSC_1H       EQU  H'FF'	; RC w/OSC2 as an IO pin (RA6)

so _HSPLL_OSC_1H have to be choose

[mischl]

thanks for your support.

my file starts so :

@ __config _HSPLL_OSC_1H

DEFINE OSC 40


i compile with the mpasm and get this error message :
[126] .. : argument out of range (not a valid config register address)

[mister_e]

NOP.... Read the bottom of your .inc file. you must write...

@ __CONFIG _CONFIG1H, _HSPLL_OSC_1H
DEFINE OSC 40

what about now

[mischl]

first i got two error messages about "overwriting previous address content" which i fixed with comment out the line "_CONFIG1H......" in 18F242.inc from the PBP root.

for testing i work with a simple programm which blinking a led. it works..., but the pause command is 4 times slower then it should be. so, it seems the pic works with the 10mhz from the external oscillator, not with the 40mhz i wish.
in the melabs programmer i've set the oscillator to HS as HSPLL too for testing, the result is the same. what can be wrong again?

thanks a lot for a support