On Sat, Aug 25, 2001 at 07:51:44AM -0400, Andy N1YEW wrote:
> Hi again

How are you?

[Trimming...]

> Andy:
> > > I've seen your page, but no idea how it helps me.
> > >
> > > I want to use HVP so i can use RB3..
>
>
> BAJ:
> > 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.
>
> Already have a supply for it.....

Even with the supply it complicates things. At minimum you have to add
a high voltage switch. Possibly a regulator too.

Again all of this IMHO. My current mode is to use a Tait style programmer
to get a bootloader into the chip. The faster, simpler, and cheaper that
activity can be done appeals to me.

>
> Andy:
> > > My circuit is directly connected on the data and clock, and MCLR is
> > > controlled by a NPN transistor.
>
> BAJ:
> > 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.
>
> Well, I tested to see how much voltage my parralel port puts out and it *is*
> 4.9V...(Pentium I 133 AT...(linux server))

So that's not the problem. You should consider adding the HCT part if for no
other reason to keep the programmer working if you ever move it.

>
> > 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.
>
> I don't think I do *especially* when it programs 16f84a's fine!

Then it's something else. What software are you using to program it?
I just uploaded my latest version of picprg2.3b to the site. It's been tested
with 16F87X and 16F62X parts. The user interface has been updated so that
the parallel port address and programming type can be specified on the config
page. Also these values are properly saved in the .picprgrc config file.

>
> > 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.
>
> I can try it but i dont think it will matter...

No. It's another issue. Let's start looking at the programming software.

BAJ
>
> Andy
> > BAJ
>
> Now I have to go buy a HCT gate at radioshack

I'd still add it even though it won't have an effect for this particular
machine.

BAJ

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