Migration from PIC18 to PIC12

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There is only 3 ICSP pins, the other 3 are Vdd, Gnd and a spare auxiliary pin. With a JDM you may not be able to reprogram the chip. The way I got around it was to power the chip from Vpp via a resistor and 5V zener but to do this you need a proper 12V supply, not one derived from the serial port.

Mike.
 
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which value of resistor? Are you trying to give Vpp external voltage of 13V in order to make pic go into programming mode right?
 
I just used a 1k resistor and so it was drawing (13-5)/1000 = 8mA from the 12V supply. As long as your Vpp can supply enough current you should be ok.

Edit, this uses the same method,
**broken link removed**

More details here.

Mike.
 
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You do have to disconnect the existing 5V supply. See the edit above.

Mike.
 
Now i am confused I do not have all the components in that circuit.

Wont it work if i connect MCLR with 12V supply + Zener + 1K resistor and connect both the grounds of 12V and my JDM burner?
 
Your Vpp is switched on and off by the programming software. So you have most of the above circuit. Do you have a schematic of your programmer?

Note, in the above schematic the four Bat42 diodes aren't needed.

Mike.
 
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No i do not have the schematic. Its actually a burner and trainer. It has several LEDs, Com port, temp sensors, 7 segment and alot of other stuff on it.

My programmer takes voltage from an external adapter of 12 V.

If the Vpp is software controlled, why don't i just add Vpp from the burner and add a zener and a resistor directly ? (The Vpp is already controlled by software so no need to worry)

am i correct of not ?
 
Yes, that is what you should do but you need to somehow disconnect the 5V Vdd supply to the chip so that it only gets 5V once Vpp is switched on.

Mike.
 
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