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PIC: Vpp voltage exceeds datasheet limit, so what?

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eblc1388

Active Member
In case any one is using/building a PIC programmer and wondering what would happen if one uses a Vpp higher than the max. limit stated on the datasheet(e.g. using 13V Vpp on a 16F914 with max. VIHH of 12V), the follow postings from the Microchip forum would give an insight into that. It is very likely that the PIC would die after being programmed 5-10 times. The guy is using two original ICD2s and different batch of PICs from Microchip. Check the posting dated 24 Sept 2005 at the bottom of the thread.

Microchip Forum post

Do not let Vpp exceed datasheet VIHH limit.
 

Joel Rainville

New Member
:shock: Thanks for posting that. From a few discussions here, I had assumed that exceeding Vpp max would only prevent some PICs from entering programming mode. In fact, I clearly remember a member here saying he was using 15V+ on MCLR to make sure the PIC would enter programming mode, although I can't remember exactly who said it?...

Since Vpp max is "only" 14V on the 16F877A, it might explain two sudden deaths during my first experiments with this PIC and my first programmer... :evil:
 

eblc1388

Active Member
The general consensus among PIC users are that PIC requires a programming voltage of 13V or higher in order to be programmed sucessfully. This must be a carry over from past experience with PICs that actually exhibited such behaviour. As such one always get the same advise in the forums, even after several generations of PIC design.

Perhaps there is still some truths in the above statement for those PICs that are one time programmable and a few 16F7XX. The question is actually quite simple. If a PIC programmed well using 12V, would one risk damaging it using 13V or higher? What's the advantage of using 13V or higher if 12V is equally as good?

One would never know for sure if one haven't tried. I have built a parallel port programmer and I'm using Vpp 12V with a 7812. So far I have no problem programming 16F628A, 16F876A, 16F877, 16F877A and 18F4455.

Have anyone tried 12V Vpp and the PIC doesn't programmed unless the voltage is raised to 13V or higher? Please post back with the PIC type so others can have a reference.

In case one wants a quick reference to the VIHH voltage limits of most common PICs, MIKE K8LH had posted a list at the end of the following thread.

PIC programming voltage limits
 

Nigel Goodwin

Super Moderator
Most Helpful Member
eblc1388 said:
The general consensus among PIC users are that PIC requires a programming voltage of 13V or higher in order to be programmed sucessfully. This must be a carry over from past experience with PICs that actually exhibited such behaviour. As such one always get the same advise in the forums, even after several generations of PIC design.
From the list posted by Mike, there are only a very few, very new PIC's which aren't specified for 13V.

Perhaps there is still some truths in the above statement for those PICs that are one time programmable and a few 16F7XX.
No, you're too new to PIC's to remember back that far :lol:

The original David Tait programmer was designed ONLY for the 16C84, which was the only EEPROM based PIC for a many years. The first DOS versions of PicProg (before it became WinPicProg) only supported the 16C84. At that time many of the OTP PIC's were programmed in a parallel mode, using far more complicated programmers.

The success of the 16C84 led to further EEPROM based PIC's, AND to the inroduction of serial programming on later devices.

The question is actually quite simple. If a PIC programmed well using 12V, would one risk damaging it using 13V or higher? What's the advantage of using 13V or higher if 12V is equally as good?
The 16C84 didn't require 10V to 13V, like many on the list, it required at least 12V, and also drew a reasonable amount of current. For programming reliability 13V became the accepted value used, as 11.9V wouldn't work, using 12V was very marginal. Using a 7812 was a problem, due to the losses through the circuit, particularly in the Vpp switching transistor. A common solution was to add a silicon diode in it's ground pin, to give a 12.7V rail - and that worked fine. The 13V solution comes about by using an 8V regulator sat on the output of the 5V one, or if you're using an adjustable regulator, 13V is a much rounder figure than 12.7V or whatever.

More modern devices no longer draw current from the Vpp line, the actual programming voltage is generated internally in the PIC, and the Vpp voltage is only used as a switching input. Assuming that is so on the new devices, I fail to see how 13V would cause any problems?, presumably MicroChip will eventually make an announcement on the situation?.

From what's been posted so far though, it's interesting that the MicroChip ICD2 uses a 13V switching voltage?.
 

eblc1388

Active Member
Nigel Goodwin said:
From what's been posted so far though, it's interesting that the MicroChip ICD2 uses a 13V switching voltage?.
Of which it is supposed to be controlled via software to stay within the max. allowable limit but an user in Microchip forum mentioned that wasn't the case because of bug in software.
 

Electrix

Member
I agree, less than 13V but more than 12V does program the PIC. I have used 2 diodes with the 7812...to get about 13.4 but when I check MCLR(bar) I get about 12.7/12.8. its probably go to do with losses in my circuit
 
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