ICSP - why must it be Schottky?

[bananasiong]

Hi,
According to the application notes of PICKit2, the diode used to isolate the Vpp is Schottky diode. Is there any reason behind this?
I'm using just a 1N4001 with a 10 khm: pull up on the MCLR for my soic PIC16F88. I was able to program for some times, just now I tried to reprogram, it showed that PIC16F88 not detected and the PIC became not working anymore. I don't use PGD and PGC for application.

Thanks.

 

[richard.c]

In basic terms a Silicon Diode 1N4001 etc gives a forward voltage drop of 0.6v.
A Schottky Diode only drops it by 0.2V.

In some situations that extra 0.4v can be helpful.

To prove if it is actually the cause of your problem just connect the Vpp direct to Mclre without the diode and 10k pullup - if this programs ok then diode may be the problem - but notice you do not mention the 100 nf capactitor.

You could also try the 470R resistor instead of the diode, but have not tried that myself.

 

[blueroomelectronics]

I use a 1N4148 diode and 22K resistor in my designs. Works fine with both PICkit 2 and ICD2 at 5V. Check your USB voltage and calibrate your PICkit 2, low target voltage might mean that 0.7V drop on MCLR is too large.
PS try programming / erasing with VPP before VDD checked with the PICkit 2 software.

 

[eng1]

it showed that PIC16F88 not detected and the PIC became not working anymore.

I've recently had some problems with the PICKIT2 software (installed on another machine). Have you tried programming the PIC through MPLAB IDE (choose PICKIT2 as the programmer)? Does it detect the PIC?

 

[blueroomelectronics]

I've recently had some problems with the PICKIT2 software (installed on another machine). Have you tried programming the PIC through MPLAB IDE (choose PICKIT2 as the programmer)? Does it detect the PIC?

The PICkit2 software really really wants .NET 1 installed.

On the other hand the PK2CMD command line version can be handy.

 

[bananasiong]

Both PICkit2 software and MPLAB IDE work well. But I prefer MPLAB directly because of.. directly
Maybe I haven't discovered the power of PICKit2 software (I'm just a newbie on PICKit2, just got it this month)

BTW, that's not the problem of the diode or anything, just noticed that one pin of the ICSP connector pad was teared out accidentally when plugging and removing the PICKit2. Everything is fine after resoldering it.

*What is PK2CMD command line?

Thanks

 

[mister_e]

PK2CMD is a DOS command line which allow to use PICKIT 2 without MPLAB. Handy if you're using a third party IDE who allow to add a custom device programmer in.

you'll download PK2CMD at the following link
https://ww1.microchip.com/downloads/en/DeviceDoc/PK2CMDv1-01.zip

 

[bananasiong]

Oh I see, but I use only MPLAB IDE

 

[Funny NYPD]

if you have more wishes to PICKit2, you can post it to Microchip forum, they will consider it and if possible you will get it in next release.

 

[bananasiong]

Thanks but I'm just happy with my current PICKit2 which is around 2 month old