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AnsweredHot!PICkit 3 performs high voltage programming without manually applying high voltage to MCLR

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pajuhesh80
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2020/07/07 08:24:06 (permalink)
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PICkit 3 performs high voltage programming without manually applying high voltage to MCLR

LVP and MCLR are disabled in my project and PGM pin of my PIC18F14K50 is connected to nothing (floating). I connected all PICkit 3 (clone but very good quality) pins to MCU except PGM; I don't need it and I don't want my breadboard to get messier! :-)
Recently, while reading datasheet, I found that I have to apply VIHH to MCLR to enter programming mode while LVP is disabled. There is no VIHH in "ELECTRICAL SPECIFICATIONS" but I found "MEMORY PROGRAMMING REQUIREMENTS> Internal Program Memory Programming Specifications> Voltage on MCLR/VPP/RA3 pin> Min. = 8V". So I think I should apply a voltage between 8-9 on MCLR to be able to program without LVP.
However, PICkit programs device successfully in HVP mode without doing so! I'm sure LVP is disabled because RC3 is working like a normal I/O and if I enable LVP, my program will stop working until I pull down the PGM.
Also, power source for both PICkit and main circuit is USB of my laptop which isn't more than 5.0V. There isn't any external power source.
Did I misunderstand something? I'm pretty sure both PICkit and PIC18F14K50 are OK.

Slow and Steady!
#1
crosland
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Re: PICkit 3 performs high voltage programming without manually applying high voltage to M 2020/07/07 10:26:31 (permalink)
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Charge pump in the PICKit.
#2
NorthGuy
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Re: PICkit 3 performs high voltage programming without manually applying high voltage to M 2020/07/07 11:41:34 (permalink)
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PICKit3 generates its own voltage. If you want LVP, you must connect the PGM pin.
 
Also, if your Vdd is 5V, you need to be careful, as the programming pins (PGC and PGD) are also USB pins and are not 5V tolerant.
#3
ric
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Re: PICkit 3 performs high voltage programming without manually applying high voltage to M 2020/07/07 13:23:48 (permalink)
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... that is, "connect the PGM pin to pin#6 of the PK3.
And if you don't want LVP, you should have a pulldown resistor on the PIC's PGM pin.
You can get unreliable programming if it is floating.

I also post at: PicForum
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NEW USERS: Posting images, links and code - workaround for restrictions.
To get a useful answer, always state which PIC you are using!
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pajuhesh80
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Re: PICkit 3 performs high voltage programming without manually applying high voltage to M 2020/07/07 23:32:47 (permalink)
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You didn't understand my question.
I said I perform programming successfully without LVP, PGM and applying 8V on MCLR. Everything is done without any error and just by USB power. My question is why does it work without applying 8V on MCLR? Is PICkit 3 generating this voltage automatically? If yes, How does it do this while power source is just 5V?

Slow and Steady!
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rpg7
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Re: PICkit 3 performs high voltage programming without manually applying high voltage to M 2020/07/08 01:32:35 (permalink) ☼ Best Answerby pajuhesh80 2020/07/08 02:18:45
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pajuhesh80
Is PICkit 3 generating this voltage automatically? If yes, How does it do this while power source is just 5V?

Yes it does.
Do a search for "single inductor boost inverter"
#6
ric
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Re: PICkit 3 performs high voltage programming without manually applying high voltage to M 2020/07/08 01:59:33 (permalink)
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pajuhesh80
You didn't understand my question.

We understood it perfectly, and NorthGuy gave you the correct answer.
 

I also post at: PicForum
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NEW USERS: Posting images, links and code - workaround for restrictions.
To get a useful answer, always state which PIC you are using!
#7
pajuhesh80
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Re: PICkit 3 performs high voltage programming without manually applying high voltage to M 2020/07/08 02:11:05 (permalink)
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ric
We understood it perfectly, and NorthGuy gave you the correct answer.

I didn't know he meaned MCLR voltage from "PICKit3 generates its own voltage." Sorry!
rpg7
Yes it does.

So why there is PGM in PICkit 3? Backward compatibility?
post edited by pajuhesh80 - 2020/07/08 02:16:00

Slow and Steady!
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crosland
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Re: PICkit 3 performs high voltage programming without manually applying high voltage to M 2020/07/08 02:16:02 (permalink)
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pajuhesh80
You didn't understand my question.

We understood it perfectly. you do not understand the answers.
 
How does it do this while power source is just 5V?



See post #2 and #3
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ric
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Re: PICkit 3 performs high voltage programming without manually applying high voltage to M 2020/07/08 04:18:05 (permalink)
4 (1)
pajuhesh80
...
rpg7
Yes it does.

So why there is PGM in PICkit 3? Backward compatibility?

To support LVP mode in old chips that do it via the PGM pin.
Having a dedicated pin for it was always problematical, and Microchip stopped doing it that way many years ago.
New programmers are still able to control it so they can program old PICs.
 

I also post at: PicForum
Links to useful PIC information: http://picforum.ric323.co...opic.php?f=59&t=15
NEW USERS: Posting images, links and code - workaround for restrictions.
To get a useful answer, always state which PIC you are using!
#10
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