trouble while programming pic16f877

Enhanced mid-range devices. PIC12F1xxx and PIC16F1xxx

trouble while programming pic16f877

Postby ukd123 » Thu May 21, 2015 5:17 pm

I am familiar with 8051 mcu.Just I am starting the said pic mcu.I programmed one a small programme on assembly.worked nice but on further expansion of that program the earlier pic mcu is not getting program, programmer is announcing 'failed at 0000h'. This try I have tried on 7 nos. pic16f877 same sequence comming only one time programming. I am doing some mistake please help. My programmer is TOP3000.
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Re: trouble while programming pic16f877

Postby AussieSusan » Fri May 22, 2015 4:32 am

Wild guess, but are you setting a CONFIG option that turns off the LVP capability when you program the chip the first time?
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Re: trouble while programming pic16f877

Postby ric » Fri May 29, 2015 11:27 am

I think that's a good guess Susan, but the opposite way.
LVP should be disabled. If it's not, and if the PGM pin is not pulled low, then programming can be randomly disrupted.
The problem will come and go, depending upon ambient humidity, temperature, and electric fields, which all affect if the PGM pin floats high enough to cause problems.
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Re: trouble while programming pic16f877

Postby Ian.M » Fri May 29, 2015 11:55 am

Worse: even if you disable LVP, the bulk erase phase of the programming reenables it, so on older PICs where /MCLR going to Vpp doesn't lock out the PGM pin, it *MUST* *ALWAYS* be pulled low during HV programming.
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