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Help with circuit(programming pics)

A

Anthony Fremont

Jan 1, 1970
0
Jon said:
Let me asky you mister smarty pants... How do you expect to program
the PIC that is "to apply the signals to teh device you want to
program"? Huh? Oh, right!!! You buy a pic programmer!?!?! Then
whats the point of using the PIC "to apply the signals to teh device
you want to program"?

That's right, you FIRST get a real programmer that works and then you can
compare your circuit's behavior to one that works.
So as you probably can't see, your argument for "a step in the right
direction" is absolute nonsense.

I'm not the one hollering for help continuously. You can think I'm a
horn-tooting dick if you want, but I've been programming PICs for over six
years. You are but one individual in a long list of people that I've seen
trod down this path at the beginning of their PIC experiences. I suggest
you sign up at www.piclist.com if you haven't already.
Sure it would help if I had a logic analyzer... and sure it sucks
working blind... but actually I have been able to program the pics.
The Pic programmer that I know work si the AN589 and does it directly
from the parallel port just fine. Actually I just rebuilt it and it
had the same problems then I removed my DMM's and put the power
signals much closer to the pic instead of far away(since its on the
bread board I spaced everything out). After that it worked fine and
I've tested it several times already with no issues.

Ok, but do you know why it works now and it didn't before?
So either my circuit works but because I had some issues that had
nothing to do with the actual circuit or something else is going on. In
any case I can now program the 18F2455 and if I wanted I could use
that to program other chips but I'll do that later until I figure out
whats wrong with my circuit.

Long skinny power leads will definitely give you headaches with a PIC. The
datasheet is very clear about Vdd rise times, if you violate them the PIC
will not come out of RESET. Also decoupling across the power pins is
necessary on the "nanowatt" parts.
You seem to think this is rocket science or something? All one has to

It's not rocket science, but then it's not a piece of cake either. If you
don't like my opinions, go ask the 3000 people at www.piclist.com. I'm sure
Olin would be more than happy to help clear this up.
do is get 4 signals from the parallel port to the pic. This isn't
difficult at all. The only problem is that the voltages have to be
fixed up and this is where the real work is. Maybe its not as dark
as you think.

It's a tad more complicated than that. As people have already told you,
rise times and timing in general are very important. Also some PICs require
Vpp BEFORE Vdd, some require it afterwards. Then there is LVP and all it
entails. Even revision 'A' parts can have major differences in the
programming algorhythm.
 
J

Jon Slaughter

Jan 1, 1970
0
Jon Slaughter said:
Seems like maybe something else was the problem. I got the AN589 working
but only after removing the DMM's and connecting the power much closer to
the pic. Is it possible that the DMM's could have caused them problems? I
was using two to measure the current drawn from the power supply and the
current from the parallel port.

I'm going to try and figure out what the problem was because maybe my
circuit was ok(except for the pullups). In any case since I have
something works I can try and work backwards "into" my circuit until I
find out what the problem was.

Thanks,
Jon

Seems to be the DMM ;/ I have a cheap one that I used(cost like 2$) and it
seems to somehow be interfering with the signals. When not used I can
program a pic chip and but when I hook it up I can't program ;/

My other DMM, which is a much better one doesn't seem to have that problem.
(well, its measuring the power supply current so not sure if it would cause
the same problem with when used on the parallel port)
 
A

Anthony Fremont

Jan 1, 1970
0
Jon said:
Seems to be the DMM ;/ I have a cheap one that I used(cost like 2$)
and it seems to somehow be interfering with the signals. When not
used I can program a pic chip and but when I hook it up I can't
program ;/
My other DMM, which is a much better one doesn't seem to have that
problem. (well, its measuring the power supply current so not sure if
it would cause the same problem with when used on the parallel port)

It's loading the pins down thru low-impedance and/or capacitance and
screwing up the shape/amplitude of the signal.
 
J

Jon Slaughter

Jan 1, 1970
0
Ok, It seems to mainly be the resistors in the circuit. 2K and below work
but above that it doesn't seem to. I'm not sure why such a low resistance is
required unless the capacitance of the pins is quite high. (slowing down the
transfer rate doesn't seem to help)

It seems that using mosfets are ok except that the when the pic is not being
programmed and if there is no shutoff method then it uses an excess amount
of current(about 30mA when not programming and 3-4mA when programming).
 
A

Anthony Fremont

Jan 1, 1970
0
Jon said:
Ok, It seems to mainly be the resistors in the circuit. 2K and below
work but above that it doesn't seem to. I'm not sure why such a low
resistance is required unless the capacitance of the pins is quite
high. (slowing down the transfer rate doesn't seem to help)

There's L in the wires too, not just C. The capacitance of the pin itself is
on the order of about 5pF. I keeps tellin' ya, it's all about the rise
times. :)
It seems that using mosfets are ok except that the when the pic is
not being programmed and if there is no shutoff method then it uses
an excess amount of current(about 30mA when not programming and 3-4mA
when programming).

If the PIC is unpowered and you apply voltage to any pin besides /MCLR (it's
special), then current will flow thru the protection diodes and onto the Vcc
rail of the PIC (and likely it's associated circuitry). If you're pushing
30mA thru the protection diodes, then you are risking serious damage to the
PIC.
 
T

Tom2000

Jan 1, 1970
0
Ok, It seems to mainly be the resistors in the circuit. 2K and below work
but above that it doesn't seem to. I'm not sure why such a low resistance is
required unless the capacitance of the pins is quite high. (slowing down the
transfer rate doesn't seem to help)

It seems that using mosfets are ok except that the when the pic is not being
programmed and if there is no shutoff method then it uses an excess amount
of current(about 30mA when not programming and 3-4mA when programming).

FYI: A Pickit2 programmer is 35 bux from Microchip.
 
J

Jan Panteltje

Jan 1, 1970
0
FYI: A Pickit2 programmer is 35 bux from Microchip.

Lots of people have been saying this, but to the defense of the OP,
I think it is good to write your own prog soft, and build your own hardware.
Anyways I went that way too, the experience obtained has more value then 35$.
And it was fun to do.
 
V

Vladimir Vassilevsky

Jan 1, 1970
0
Jan Panteltje wrote:

Lots of people have been saying this, but to the defense of the OP,
I think it is good to write your own prog soft, and build your own hardware.
Anyways I went that way too, the experience obtained has more value then 35$.
And it was fun to do.

Totally agree. Besides, it is much better to learn by fixing the
mistakes of your own rather then live with the bugs and the
inconveniences created by somebody else.

VLV
 
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