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Internal Oscillator and Internal MCLR

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thecritic

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I need to use MCLR as input pin and I need to use internal oscillator.
Why does MPLAB warns me for trying to doing this?
I hear that if I do so, I can no longer be able to re-program the device as MCLR is internal and programmer can't take control of it. But why would using Crystal Oscillator allow to do so? What is the work-around?

Thanks.
 
Most of the newer chips can handle this if you have a programmer that can do Vpp before Vdd.

Mike.
 
Do, Vpp before Vdd? Does this means, I have to power the Chip through PK3, so as to provide it control on Vdd?
My chip is PIC16F676
 
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Also, Is there some work-around to program the device in its own target circuit. (I can't power the target circuit by PK3). I hear somewhere that introducing delay loop may work. But since, I can always re-program it in Isolated mode by powering through PK3, I am safe to and so will experiment.
Thanks Pommie and Nigel.
 
Why don't Crystal oscillator pose the same problem? I am curious.

It does - except you can kill an external oscillator - you can't kill the internal one.

Basically if the PIC starts running, you can't then access programming mode - so you MUST access programing mode before it has time to run. You don't actually need Vpp before Vdd, you just need Vpp before it runs.
 
Oh! wow. I used Internal Oscillator and Internal MCLR. I separately powered the target. The target was running. I then connected PK3 to the target. Still the PK3 programmes it smoothly.(It warns me everytime though!)
So, it wasn't that bad as it as been publicized! Perhaps, I was Lucky! :)
 
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It might be an old pic but the PK3 is definitely a new programmer that has circumvented the problem.

Mike.
 
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