re=programming a chip with PLL H4 enabled?

valemike · Guest

I am having trouble programming an 18f448 chip with the Microchip ICD2 on a chip that was previously programmed with the PLLx4 fuse bit set. The other 18f448 PIC in my board erases and programs just fine.

I tried it on another board, and the same thing happens.

All attempts to erase the chip fail, as well as programming it. The program in flash in fact remains untouched.

Is there an issue with re-programmability of previously programmed PICs with H4 enabled?

PCM programmer · Joined: 06 Sep 2003 Posts: 21708

What's the Vdd voltage on the PIC ?

If it's 3.3v, then there's a few threads on the subject, some
of them with some screaming.

On edit:
This problem is supposed to only apply the code protection bits.
You can only erase them with a "bulk erase" and that can only
be done with Vdd at +5v.

But, if you're using 3.3v, I think it's worth it to try +5v (if possible)
and see if it solves the problem.

Mark · Joined: 07 Sep 2003 Posts: 2838 Location: Atlanta, GA

Also try it with the power supply plugged into the ICD2

treitmey · Joined: 23 Jan 2004 Posts: 1094 Location: Appleton,WI USA

I think there was also a problem/feature that the power needs to be turned off and back on. I think it was something to do with the 4x PLL

dyeatman · Joined: 06 Sep 2003 Posts: 1923 Location: Norman, OK

Yeah, that one is where the chip PLL will not kick in until you cycle the power after the programming.

valemike · Guest

Voltage to the PIC was 5V.
I didn't have power connected to the PIC; rather it comes from the ICD-2.

I already resolved my problem. Apparently, the diode i have hooked up to Vdd was causing the voltage applied by the ICD-2 to go down.

I took out the diode and all is fine.