2019/12/08 07:38:53
Wanglesnap
It has been recommended to use a 100R ballast resistor on MCLR on some PICS ,any thoughts on this like will it cause damage? , can I use it for all PICS by leaving it in my programming lead?,I am using a 3watt it just gets warm.
Thanks
2019/12/08 10:00:11
Mysil
Hi,
100 Ohm sounds wrong, and 3 Watt resistor getting warm is definitely wrong.
What have you actually hooked together? Schematic!
 
A 100 Ohm resistor in series in the line between MCLR pin and programming connector may be O.K.
When the programmer tool is disconnected, it will be open-ended anyway.
 
The MCLR pin should be pulled up to Vdd power line by a 10 kOhm resistor.
Some PIC devices have internal weak pull-up that may be used instead of external pull-up resistor.
 
If there is a Reset switch, and or a Capacitor connected to the switch, some datasheets show such circuits,
then there should also be a resistor with value between 470 Ohm and 1 kOhm,
between switch/capacitor connection, and MCLR pin.
This serve 2 purposes: 
1: Preventing any bouncing current from switch and capacitor from causing undershoot voltage on MCLR pin.
2: Signal isolation when Programmer tool drive the MCLR pin for Reset or High voltage programming.
If there is Reset button, there should still be 10kOhm pull-up resistor from switch to Vdd supply.
 
These are all my opinions,
    Mysil
2019/12/08 12:25:42
ric
Wanglesnap
It has been recommended to use a 100R ballast resistor on MCLR on some PICS

Where did you see this?
I am guessing you have been reading about problems some people have had with PK4 and ICD4 when used with old PIC's that require 13V Vpp, and the resistor wired in series with VPP/MCLR is suggested to limit current.
Context is vital here. It matters what chips you are programming, and what programmer you are using.
 
As Mysil said, if you have a 3W resistor mounted somewhere, and it is getting warm, then there is something very wrong!
2019/12/17 09:44:10
Wanglesnap
Sorry late replying, you hit the nail on the head it has been recommended for some old pics but I'm learning on old pics like 12f508,16f628, etc. These chips were getting quite warm and failing during programming but the resistor seems to have stopped this. I am going to recheck after mplabx v5.30 upgrade.
2019/12/17 09:49:06
Wanglesnap
I should mention I program with pk4 and a zif stand-alone programmer with 20k pull up.
2020/11/18 06:44:21
Lucky Luka
Is there a list of these "old" PICs? Is PIC18F4580 considered old? I don't want to brick it and waste time. I have used pickit 3 so far and I was thinking of upgrading to pickit 4. https://www.youtube.com/watch?v=s4IgVmhHbAc
2020/11/18 07:17:58
NorthGuy
Lucky Luka
Is there a list of these "old" PICs? Is PIC18F4580 considered old? I don't want to brick it and waste time. I have used pickit 3 so far and I was thinking of upgrading to pickit 4. https://www.youtube.com/watch?v=s4IgVmhHbAc



As far as I know these were PIC16 where Vpp is 13V. PICkit4 caused voltage overshoot which was killing PICs.
 
PIC18F4580 has Vpp specification 9-13V, so hopefully PICkit4 doesn't use 13V (easy to check with a scope before connecting to the PIC). At any rate, you can use LVP mode which doesn't require high voltage, so it's perfectly safe. Or you can use the serial resistor, just in case.
2020/11/18 09:50:57
Lucky Luka
If PIC16's  VPP = 13V and my PIC18's = 9-13V where is the difference?
If I were to leave that 100 ohm resistor, pickit3 would not be able to program correctly, right?
2020/11/18 11:15:47
Mysil
Hi,
Documentation is just where it should be,
In the product webpage for the PICkit 4 programmer tool.
https://www.microchip.com...roductDetails/PG164140
See Documents Tab
http://ww1.microchip.com/...shoot_modification.pdf
Also note this in the rework document:
"NOTE: If your MPLAB PICkit 4 serial number is BUR20xxxxxxx or later, you do not need to apply this ETN."
 
For PICkit 3, it is my understanding that 100 Ohm resistance in series in /MCLR/VPP line, 
should not cause a problem. The IPP current is small, typically 1 mA.
I think there is no harm trying.
 
On the other hand, my question would be:
Since the PICkit 4 have som way of controlling the VPP voltage from firmware for other devices,
Why cannot this be solved in firmware, by ramping up the voltage more gradually?
And be distributed for all PICkit 4 in a MPLAB X release?
 
    Mysil
 
2020/11/18 11:23:40
NorthGuy
Lucky Luka
If PIC16's  VPP = 13V and my PIC18's = 9-13V where is the difference?

 
The difference is in the level the programmer chooses to apply. 9V works fine. 13V may not.
 
Lucky Luka
If I were to leave that 100 ohm resistor, pickit3 would not be able to program correctly, right?



I think PICkit3 will be fine with 100 Ohm resistor.
 
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