On Fri, Aug 24, 2001 at 11:35:13PM +0000, Andy Kelley N1YEW wrote:
> Hi
>
> Byron A Jeff writes:
>
> > On Fri, Aug 24, 2001 at 12:14:22PM -0400, Andy N1YEW wrote:
> > > I am trying to convert linuxpp(david tait style hardware) from the 16f84 to the 16f87x....
> > >
> > > What would I have to change to make it work??
> > >
> > > I saw that BAJ said that(http://piclist.com/techref/microchip/16F877/taitlinux.htm):
> > > "The final patch to picprg 2.2 is changing the 0x08 begin programming command in lowlvl.c to 0x18, which is the 16F87X equivalent."
> > >
> > > I tried that but it still couldn't erase my new 16f876...
> > >
> > > Any suggestions?
> > >
> > > YES, RB3 is tied to ground!
> >
> > Oh that was long ago! We've had several threads since then on the subject.
> >
> > Let me suggest you try my trivial programmer. Essentially it's the Tait
> > programmer with all of the high voltage stuff removed. Only does low voltage
> > programmer. It's been tested with the 16F87X series and the 16F628. My
> > development environment is Linux based but as long as the software has
> > configurable pins, anything should work:
> >
> > http://www.finitesite.com/d3jsys
>
> I've seen your page, but no idea how it helps me.
>
> I want to use HVP so i can use RB3..

Sometimes I know the feeling. I really wish that Microchip could have found
one end or the other of Ports A-C to stick LVP on. I don't really miss the pin
but its location sucks.

But usually I've found it just isn't worth the effort. While 5V is easily
findable on a PC, that 12V signal usually is only available from either the
serial port or a disk connector. Point is that you have to hunt it up.

>
> My circuit is directly connected on the data and clock, and MCLR is
> controlled by a NPN transistor.

I'd advise that you actually measure the output voltage of your parallel port.
This is where my page does really help. I've noticed that modern ATX
motherboards will often only output a high of 3.3V to the parallel port.
Perfectly legal since a TTL high signal only need be 2.0V. But by spec the
PIC must be programmed with a Vcc of 5V. And at that voltage 3.3V is undefined.
An input must be a minimum of 0.8Vcc to be considered high and at 5V that
value is 4V.

You'll probably need a HCT part as I describe on my page in order to guarantee
the proper signal level. It'll convert that 3.3V TTL high in into a CMOS Vcc
out. You'll probably have the same issue with the transistor not snapping
completely on.

As soon as I added the HCT part on my trivial programmer it started working
like a champ. It also guarantees that your programmer will work with any
parallel port.

BAJ

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