[SOLVED]Problem with 18F97J60

loggin · Joined: 23 Sep 2010 Posts: 10

Hello everybody!
I got a problem with this chip. It can't run at any other oscillator frequency except its own internal! I have been searching many topics about this problem - and all look like the same! I have tried 3 compilators, the result is more than disappointed!
I tried with other chip - the same. I want to drive it with 25MHz oscillator.
I put 100nf caps at every Vdd-Vss pair. Vcap - 10uF (internal regulator).
Maybe the problem is somewhere in my PCB. I have tried very different FUSES - and nothing happened.
The program that I want to try is very simple - just blinking LED.
Thank You in advance!

Ttelmah · Joined: 11 Mar 2010 Posts: 19539

Describe your PCB, round the oscillator pins?.
What crystal have you got?. Frequency, and _type_ (preferably a part number and supplier (you say '25MHz')).
What load capacitors are you using?.
How long are the tracks to the crystal?.
How is the ground plane run near these legs and tracks?.
Are you using a crystal, or an oscillator?.

Best Wiishes

loggin · Joined: 23 Sep 2010 Posts: 10

Thank you for the fast reply.
I use crystal SJK 25.000. Load capacitors are 33pf. The length of tracks to the crystal is about 8-10mm. The ground track runs between the pins of the crystal. I've tried other placements but nothing different.
Regards!

asmallri · Joined: 12 Aug 2004 Posts: 1635 Location: Perth, Australia

You have not given specific enough information to be able to identify the specific crystal you are using. I have implemented a few designs with this PIC with capacitors in the range of 18 to 22pF - naturally it depends predominantly on the crystal.

I suggest you look at the fuse settings and your programmer to make sure you have not inadvertently told the programmer to ignore the fuse settings in the code.
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loggin · Joined: 23 Sep 2010 Posts: 10

I've changed fuses on program and programmer but nothing. Got tried with variable values of capacitors - the same! Even though thank you for the advice!

ckielstra · Joined: 18 Mar 2004 Posts: 3680 Location: The Netherlands

We want to help you, but you have to provide more info. "crystal SJK 25.000" is not enough. When I go to the SJK website I see many different crystal types and each can have 16pF, 20pF, 30pF, 32pF or other value series capacitance.

- Post a schematic.
- Post your small but complete test program
- Post your compiler version number.

loggin · Joined: 23 Sep 2010 Posts: 10

The crystal is this one - http://www.q-crystal.com/upload/4/2009436173132156.pdf

Here is the scheme: http://www.picvalley.net/v.php?p=u/2614/51461038614276210071285319267juxFUSmKZ006MvGxBLU9.PNG

Programme:
main.c

Ttelmah · Joined: 11 Mar 2010 Posts: 19539

The crystal will be something like SJK-6B 25.00 xx yy zz F q nn
It is these later figures we are interested in.
Now the xx figure is critical (load capacitance). yy (tolerance) will only matter if you are worried about the accuracy. Similarly the later figures (temperature range, height etc.., shouldn't affect things too much. So you need to look at the invoice, and find what you actually have, for that first number.
Similarly, for the 'F'. At this frequency, these crystals are available as fundamental, or third overtone devices (F or 3). You should have 'F'.

Pull the application note from Microchip, about PIC crystals. You talk about the ground plane 'running round the crystal pins'. If so, this may be your problem. Though ground planes are great for reducing noise, they introduce significant capacitance problems at high frequencies. Depending on the gap you have selected, which side of the board the tracks to the crystal are on, and the specified load capacitance of the crystal, you may have more capacitance already present from the ground plane, that the crystal is designed to operate with... The 'normal' way to work round the crystal, is to have a hole in the plane, with a 'ring' of track outside the crystal/PIC legs, which is then coupled to the ground plane.

Identify the crystal properly, and post a picture of the PCB section round the crystal (and PCB material).

Best Wishes

loggin · Joined: 23 Sep 2010 Posts: 10

I read before about the crystal but there's nothing written except SJK 25.000!
About the board-I use a test board but I thing this is not the problem.
However, thanks to all for the answers!

loggin · Joined: 23 Sep 2010 Posts: 10

At the end - it's solved.Thanks to all of You for the advices!!!

bkamen · Posted: Tue Oct 19, 2010 9:56 am

loggin · Joined: 23 Sep 2010 Posts: 10

Due to I use a test board for this project, I use wires to connect pins to other points or buses. The wire to the 59th pin (Vdd) evidently was not soldered very well (*devil*). I had to resolder the junctions to the pin one by one to find where is the problem. And almost always the problem is something little little hidden for the eyes in the first look.... Thanks to all for the patience......Cheers....Regards....

KU5D · Posted: Fri Oct 22, 2010 9:09 am

My issue is just the opposite. I've used internal osc on other chips (18F4525 and 8527) with no problem, but cannot get the 97J60 to run on anything but an external crystal. #FUSES INTRC seems like the only change I made on the others, but that's not the case here it seems. Am I missing something simple?
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bkamen · Posted: Fri Oct 22, 2010 9:12 am