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'[PIC] Problems with NOPPP and PIC16F84A'
2007\03\01@190420 by Joseph Marlin

picon face

  A few months ago I ordered some PIC16F84As and have since been trying to
build a programmer for them. I have decided to use the NOPPP design (
http://www.covingtoninnovations.com/noppp/ ), however I am having the same
problem with this design as the COM84 design I tried prior to NOPPP (which,
I found too late, does not support the A version of the '84). The problem is
that no matter which of my '84s, software (FPP, NOPPP programmer and PIX),
parallel port or operating system I use (XP and 95), the PIC can be erased
and read but not programmed.  

  I have checked and double-checked my circuit against the schematic and
even run through the circuit testing utility of the NOPPP software, but they
all tell me my circuit is working perfectly. The only thing I can think is
that perhaps, though the NOPPP website claims otherwise, the NOPPP is
incompatible with the '84A. If anyone has any input on my delemma, I would
appreciate it very much.
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2007\03\02@060229 by Byron A Jeff

face picon face
On Thu, Mar 01, 2007 at 04:04:18PM -0800, Joseph Marlin wrote:
>
>    A few months ago I ordered some PIC16F84As and have since been trying to
> build a programmer for them.

PIC 16F84A are obsolete for new designs. While they may be OK for building
something that's already in the can, if you plan to design something new,
there are much better offerings in both the 16F and 18F families of parts.

> I have decided to use the NOPPP design (
> http://www.covingtoninnovations.com/noppp/ ), however I am having the same
> problem with this design as the COM84 design I tried prior to NOPPP (which,
> I found too late, does not support the A version of the '84). The problem is
> that no matter which of my '84s, software (FPP, NOPPP programmer and PIX),
> parallel port or operating system I use (XP and 95), the PIC can be erased
> and read but not programmed.  

What voltage does the serial port generate? All of the serial port designs
were designed to work with true blue EIA-232C serial ports. PCs haven't had
such serial ports in close to 10 years. Many PC serial ports only generate
voltages of 0 to 5V, with some generating voltages as low as 3.3V.

>    I have checked and double-checked my circuit against the schematic and
> even run through the circuit testing utility of the NOPPP software, but they
> all tell me my circuit is working perfectly.

Again what's the Vpp voltage at PIC socket. If you're using 16F84A's and that
voltage isn't 13V +/- 0.5V then it isn't going to program. Also IIRC the
16F84A has a whopping huge programming current. I checked out the programming
specification. 50 mA! OUCH!

No serial port in the world is going to provide 50 mA of current at 13V.

If you're serious about pursuing this design, I'd advise adding a external
13V power supply to provide Vpp.

A better idea is to abandon the 16F84A and step up to a newer part. Virtually
every current part uses flash that programs at 4.5V, so the Vpp is a low
current signal.

Good Luck.

BAJ

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