[PIC16F] Baked chips,anyone ?

Hello folks !
I've just moved from AtMegas to PICs.And I just baked my first 877As.
I suspect this was because of faulty board design,as some other thread here states that isolation of ICSP pins is needed,which was lacking.

I made a simple board (a 4 digit counter with 7 seg LEDs) with 16f877a as the uC.
I did not isolate the PGC (which goes to a LED via a resistor).There's nothing connected to PGD,and MCLR is pulled up to Vcc by a 4k7 resistor.The GND and VCC pins were connected to programmer directly.

So when I connected the programmer,the PIC burned out.
Later,I tried to program another 877A (using the ZIF on my USB programmer) but the programmer was connected to that board via ICSP,and then a BC557 on the programmer popped out like a popcorn

So can you people please tell me the appropriate way to isolate the ICSP pins? Or do you believe this problem can be because of any other reasons ?

Please pardon my paranoia,I'm on a schedule here and I never expected my desk to look like a kitchen platform.
Thank you so much !!
:smile:

Hi,

Baked beans and chips - hmmm, just ready for a snack:-D

If you see this pdf from the Pickit2 manual it shows how to connect your ICSP.

The 4K7 you have on Mclre might be too low, so up it to 10k.

You can isolate some circuitry from the programming pins by resistors but doubt you can do that with a heavy current leds.

On a 40 pin chip like that I always ensure the programming pins are free, the only other practical alternative is a simple dp isolation switch which you can use on both pins.

I found the PIC 16F877A and 16F877 some what fragile. I have damaged several of these while programming on the PICSTART plus programmer.

Whereas I never had such problems with 16F648A/16F628, 16F690 or the 18F series.

I think the 877 series is more susceptible to damage than the others. Probably design fault or something makes this happen.

arbj said:

I found the PIC 16F877A and 16F877 some what fragile. I have damaged several of these while programming on the PICSTART plus programmer.

Whereas I never had such problems with 16F648A/16F628, 16F690 or the 18F series.

I think the 877 series is more susceptible to damage than the others. Probably design fault or something makes this happen.

Click to expand...

Hi,

Have to disagree there - have used the 16F877A and the rest of the chips, 873 / 876A, in that family for many years with various programmers and found them bullet proof.

On the other hand the 628/628A does have strange problems.

Think a lot of problems occur because things like the Config settings, poor diy programmers/software or users circuit designs are incorrect.

may be you guys encountered duplicate chinese micro conttrollers

Thank you people. My board is up and running now. I've given up on the idea of using ICSP and am now programming the chip first and then putting it into the ckt. Tedious,I know.
@wp 100 : Yeah,programmer quality makes a world of difference. You all probably already knew it,but I'm learning the hard way now. I'm using a cheap clone that can program correctly only if the configuration bits are specified in the code. I wasted an entire day because I was flashing the code first then separately programming the config word-and then the PIC won't start up.
@arbj & welove8051 : 877a seems pretty sturdy. ESD hasn't been a problem even after my rather rough handling for a week now. I even (accidentally) reversed VDD and VSS for a few seconds and it survived!
Cheap chinese controllers,though,are an epidemic here (India) - I have to make significant efforts to ensure authenticity.

Hi,

Well sounds like you have a Pickit2 clone so that should work fine with a 877A.

You are always better to include the Cofiguration code and EEProm Data in your main program code and burn it all together - never had any problems doing that.

You can often find that the Pk2 seems to behave strangely with weird error messages, like need to download program etc, but this is usually down to the users doing things wrong, once you do things correctly its as simple as abc, really !

ICSP works fine given the basic connections detailed in that Pk2 pdf.
On a 877A you must have both pos pins 11/32 and both neg 12/31 pins connected and just a 100nf across them, not some massive electrolytic.
If you cannot reorganise your code so RB6 and RB7 programming pins are free, then a simple double pole switch can be used so you just switch over to programming mode or run mode on pins RB6&7

Its well worth sorting that out for two reasons, if something is burning out your Pk2 / 877A you have a serious wiring /component problem still around, plus you will find the Pk2 Debugger a very useful tool to use as your code becomes more complex, it uses the same connections as ICSP.

The vital thing in ISCP circuitry is on page 21 in **broken link removed**. I've never tried to replace diode with 470R resistor (once i bought like 300 BAT54's at total bargain so why bother ;p). Although I can tell you that not using the capacitor shown in the schematic would sometimes cause serious stability issues. Some PICs (i think 18F are more susceptible than 16F in general) would reset because of even very short pulses on MCLR line. And after releasing from reset if some 'ringing' occured sometimes the uC would reset like 4-5 times before starting for good.

Conclusion: use the schematic above and everything should be fine.