PIC18F4431 won't start up

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jeanxxx

Joined: 24 Dec 2004
Posts: 4

24 Dec 2004 2:25 PIC18F4431 won't start up

Hi guys,

I'm currently using a PIC18F4431(I've used a PIC16F877A before).

My design is very simple, a 20MHz crystal with 2 15pF caps and 8 LEDs at PortB.

Vdd, AVdd and MCLR pins are pulled to 5V and Vss, AVss pins are pulled to ground.

I've written the software using ASM and programmed it using MPLAB ICD 2

I've set the __CONFIG 1H register such that the chip is operating in HS mode.

However, when I power up, the chip won't start at all. I tried to look at the signal at the OSC2/CLKO pin and I find that there isn't any clock pulse generated by the internal oscillator. Crying or Very sad

Later on, I tried to put a cap from Vdd to GND but still it refused to start up. Crying or Very sad

Can anyone give me any advice on how to solve this? Any feedback will be much appreciated. :sm27:

Thanks in advance.

Regards,
Jean

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XNOX_Rambo

Joined: 13 Jul 2002
Posts: 437
Helped: 87
Location: Far out, man!

24 Dec 2004 3:20 Re: PIC18F4431 won't start up

MCLR is active low so if you pull it to Vss (if that is what you are saying) then
you are applying a continuous reset.

/Rambo

jeanxxx

Joined: 24 Dec 2004
Posts: 4

24 Dec 2004 9:13 Re: PIC18F4431 won't start up

NO, the MCLR is pulled to 5V
i mean Vss and AVss are pulled to GND

thanks anyway RAMBO

Jean

XNOX_Rambo

Joined: 13 Jul 2002
Posts: 437
Helped: 87
Location: Far out, man!

24 Dec 2004 14:14 Re: PIC18F4431 won't start up

Sorry, it was very late so I misread your sentence... Wink

Anyway, the oscillator should be running even if the reset pin is active, so
the only other thing that comes to mind is that the PIC has found the SLEEP
command in your code - and gone to sleep.
Or then it it just might be broken.

Sorry, but that is all the advice I can give.

/Rambo