MCLR required before code runs

[Jerry R]

I am working with a 18F452 and am having a problem with the code not running before a "hard" /MCLR is issued after power-up. I don't think Vdd voltage rise is an issue since I've tried powering-up with a "cold" switch from Vdd. When connected, an ICS U40 debugger starts code fine.

The target hardware is the same as with other older project completed successfully.

Any help is much appreciated.

[Ttelmah]

Have you got the 'PUT' fuse in the new code?. If not, try adding this. You say the hardware is 'the same', is it actually the same hardware, or a dulicate?. If the latter, double check the capacitors used on the crystal. You can get this behaviour if these are too large, it prevents the oscillator starting properly, with the supply rising. Even if the hardware is the same, check these, since chips do differ, and the one you now have, may be slightly more fussy.

Best Wishes

[treitmey]

Also the PLL will require a power off before it works. but only after the first time the fuse h4 is set.
.... edited ....
after seeing that you tried a cold power up. PLL would not be the problem.
......
perhaps you only think that it is not running. ((but it is)) if you don't see the
proper serial data,.. except when the icd-u40 is connected, then i would think that the issue is that the icd-u40 is providing the ground for serial com.
without the ground, you don't see the data.

[Guest]

Thanks for all the replies! I should have looked more closely at the fuses!
Regards