oscillator problem

[Acetronics2]

The only thing to watch when overclocking is that things like serial comms ad the like often wont work. I had an 18F4580 running on a 20Mhz xtal with the HS_PLL setting - whilst it wasn't probably running at 80Mhz, it was dammed fast - but non of my serial comms would work until I replaced the 20Mhz xtal with a 12Mhz one. (as spotted by Alain)

I was going to suggest that you tried using the xtal from the breadboard that you know was a proven crystal... but now you seem to of resolved the problem. - I have to agree with Alain, I would only purchase from a large component retailer (RS in my case).

Hi, Malc

your problem was setting correctly the OSC related registers ... not a Xtal problem ...
as you were running @ ... 4x 12 Mhz !!!

for PBP ... it is not overclocking, as those frequencies are in the compiler's list ...

@ Kamikaze

looks there's a supply stability or glitches problem that doesn't allow the PLL to stabilize quickly ... add a 10/22 µF Tantalum bead as close as possible to the PIC !!!

You also can poll for the PLL stability flag before allowing your program to run ... ( for execution sake )

Alain

[Kamikaze47]

looks there's a supply stability or glitches problem that doesn't allow the PLL to stabilize quickly ... add a 10/22 µF Tantalum bead as close as possible to the PIC !!!

The only SMD tantalum cap I had handy was 1uF so I soldered it as close to the pic's supply pins as possible and it seems to have fixed the issue.

I'll know for sure once I've left it off night and turn it back on.

Thanks heaps for your help.

[Acetronics2]

The only SMD tantalum cap I had handy was 1uF so I soldered it as close to the pic's supply pins as possible and it seems to have fixed the issue.

I'll know for sure once I've left it off night and turn it back on.

Thanks heaps for your help.

Glad you finally see the end ...

Et ... YES, PLL's are very sensitive to supply !!!

[Kamikaze47]

still no luck unfortunately

when i turned it on after it being off over night, it took 3 mins to start running.

once it was running it seems to work fine, and turning it off and back on results in a quick start up.

the time it takes to start seems to be proportional to the time that it's been off.

[rsocor01]

still no luck unfortunately

when i turned it on after it being off over night, it took 3 mins to start running.

once it was running it seems to work fine, and turning it off and back on results in a quick start up.

the time it takes to start seems to be proportional to the time that it's been off.

I am not sure if you have mentioned this before. Are you using a voltage regulator? Where are you getting your supply voltage from?

Robert

[languer]

A few pointers:

• Can you make a simple program to just blink an output - nothing more?
• Can you make this simple program run with; (1) internal 8MHz osc and x4 PLL [32MHz], (2) external 10MHz osc and x4 PLL [40MHz]?
• Your ground return lines on the PCB look questionable. Looks like you could've used a ground plane, but you chose to run lines back to the connectors. The crystal capacitors are expected to have good ground connections and the PCB does not appear to accomplish this.
• Simple code and possibly a schematic would go a long way to help troubleshoot this. Best guess at the moment is that the PCB is not close to ideal.

[malc-c]

To be honest I'm finding it hard to work that PCB out - I guess the copper is the top layer as it's surface mount ? - without the component overlay we could make assumptions that the two large components are capacitors and the component that sits over the top of what looks like capacitors could be a regulator..... just guessing

To the OP - you stated the circuit worked fine when breadboarded - try re-building it on vero strip board using descrete components (possibly the ones used on the breadboard) and see if that works. If it does then it would suggest that the problem is with either the PCB design or the SM components.

[Kamikaze47]

I am not sure if you have mentioned this before. Are you using a voltage regulator? Where are you getting your supply voltage from?

I have tried 2 difference sources. Firstly a computer power supply's 5v rail, and ive also tried the 5v source on the pickit2. No regulator.

To be honest I'm finding it hard to work that PCB out - I guess the copper is the top layer as it's surface mount ?...

The blue is bottom layer - all surface mount components are on the bottom layer. The through-hole components are on the top layer. Even though it looks like components are on top of each other, they are actually on opposite sides of the board.

I realise that the PCB isn't self explanatory, sorry.

A few pointers:

• ...

I will try the things you suggested and post back.