how to reprogram 12f675 and 12f629 ?

[iw2fvo]

hi to all of you in this forum,
I programmed some 12f675 and 629 and I reassigned the pin that are normally used for programming the chips.
MCLR, PData and PClock do not have their function anymore.
I have to reprogram those chips but the PicKit_3 does no longer recognise the chips. So they bicame like an OTP !!!
I follow some instruction found on the net and suggested in the forum but with no success.
Any proven procedure available to recover the chips please ?
Thanks in advance.
regards,
Ambrogio

[mackrackit]

I will guess that you have the chips in circuit and the three programming pins are connected to something.

You will need to disconnect the three pins or in some way isolate them from the remainder of your circuit.

Then you should be able to re-flash them.

[richard]

vcc may need to be 5v also , and sometimes its best to let the pickit provide the power

[iw2fvo]

Thanks,
The three programming pins are connected to the PicKit only.
The 5vdc is applied to the PIC by the circuit : PICKit does no suuply power to Pic.
No way for now to recover them.
Bye
Ambrogio

[iw2fvo]

I forgot to say that I have read and applied those instruction:

http://www.microchip.com/forums/tm.aspx?m=303686&mpage=2&key=&

Ambrogio

[richard]

PICKit does no suuply power to Pic.


that's my point , the pickit needs to provide the power . timing is critical in getting the chip into programming mode

[richard]

vpp must be asserted before vcc to enter pgm mode


see this for the reason that the pickit must supply the power if your interested [figure2.2]
http://ww1.microchip.com/downloads/en/DeviceDoc/41191D.pdf

[mackrackit]

Ambrogio,

I am curious as to how you reassigned the functions of these pins. As far as I know it is not possible. The pins can be used for other things such as MCLR can be used as an INPUT, but if programing voltage is applied it is once again part of the programming chain.

[iw2fvo]

thanks Richard,
Are you saying I have to remove the power to the PIC (target ) and supply it from the PICKIT only ?
I forgot to tell that if I connect a brand new pic12f675 everything goes well ...
Thanks again.
Bye,
Ambro

[richard]

Are you saying I have to remove the power to the PIC (target ) and supply it from the PICKIT only ?

there is no other way to get the chip into prg mode if the mclr pin is assigned as an input pin


I forgot to tell that if I connect a brand new pic12f675 everything goes well ...

a new chip has a mclr pin