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'PIC16F877 programming question'
2000\04\03@223347 by naxel

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Hi to all PIClisters,

I have recently developed a PIC programmer based on Taits' design.
Everything went fine for the PIC16F84. The problems occured when I tried to
program a brand new PIC16F877. The programming process was completed
successfully (or so it seemed). The initial test code was supposed to set
TRISB to output and drive some pins of PORTB high (turn on some leds). The
glow of the leds was faint, so I checked the voltage of the pins. To my
surprise, high pins were at 2.4 Volt. Later on, I read about the LVP option
of the chip, and my guess is that I tried to program it in this mode, using
my high voltage programmer, and fried the ports. I have also read that LVP
can be disabled by clearing the 7th bit of the configuration word, but I
can't see how this may be achieved, without a low voltage programmer at the
first programming attempt. To my understanding, this has something to do
with the RB3 pin, but since the fried chip was the first one of the only
pair I have, I would not like to risk the other and learn the hard way.

Is there a recommended programming procedure for programming a PIC16F877 for
the first time (in order to disable the LVP from the configuration word),
using a high voltage programmer (12-14 Volt) ?
I would be grateful for any relevant help, advice or reference (or good news
for the fried chip :) ).

Thank you all in advance.

Nicolas Axelos
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2000\04\04@112255 by M. Adam Davis

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Chances are slim that you fried the chip as long as you had it hooked up
correctly.  The programming voltage (13v) is only applied to the MCLR pin, and
none other.

I wouldn't be too surprised if your pins were oscillating (very fast) giving you
about 2.4 volts (conveniently 1/2 of 5 volts.  50% duty cycle?), and dim LEDs.

Did you use a program which is meant to program the f877 with a tait
programmer?  Programming the f877 is not the same as programming the f84, and
you need to use different software on your PC.

Assuming you have used the right connections for the programmer and the right
software, go through the instructions for building the programmer again and
check all the voltages and connections.

I hope this helps.

-Adam

naxel wrote:
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