Vpp Values in PIC !!!!

[Mohammad_Yhaya]

Peace be upon you
dear friends , i'm working in DIY usb pic programmer "usbpicprog", and after finishing it's fabrication , i load a boat loader in it ,
the PC recognize it verywell, i upgraded the firmeware , it's fine,
the problem is ...... no pic is detectable ,,,,
i tried many pics ,,, 16f877a , 18f4550, 18f2550 .... no pic is detected.
and if i chose the pic manually ,,,, it didnot pass the verification test after write the code " means no code is written".
i run the pin test on UsbPicProg , it seems every thing is fine except the Vpp voltage .
when i chose 12 V the pumps give me only 8.5 Volt ,,,,
i don't know if this is a good Vpp value for programming pic , or not?
i searched every where about the exact Vpp value for pics in datasheets, but i didnot find any spacific vuale for Vpp ,,,,,,,
can you help me to determine if the problem related Vpp or or not ?? and any ideas to fix it ????
thanks

 

[FvM]

You'll want to review the dedicated Flash Microcontroller Programming Specification at microchip.com.

A typical Vpp specifcation is VDD+4.0...12.5 V.

 

[Mohammad_Yhaya]

peace be upon you
dear FvM thanks very much
yes ,, i add 1.5 volt dc battery in series between Vpp cable "from usbpicprog" and "Vpp PIC pin" so the voltage rise form 8.5 to 10 volt and it's work fine,,,,
so i think taht the problem was from the voltage pump " the Vpp voltage producer",
but i don't know why is that !!!!! 8-O ???
and how can i rise the produced voltage to eleminate the dc battery :-? ???

 

[Mohammad_Yhaya]

peace be upon you
the soldering ............... it was not good ,,,, i fix the miss ,,,, every thing is fine now ,, no more need for external battery ,,,
also ,,, i add a zener cuse the voltage go over 12 DC ,,,, many thanks for helping