I'm soooo close with this.

Thanks to Olin's comments yesterday and his ICSP document I can program
the PIC in-circuit, on my bread-board, perfect.
Sent a flash LED type program and all is ok.

However, to get the circuit to run, I have to disconnect the link from
the PIC's MCLR pin to the programmer cable (I can leave all the other
signals connected). It looks like the programmer is dragging this signal
to GND.

I currently have a diode and a 22K resistor from the MCLR pin to +5v
I tried reducing this to 1K but still have the same problem.

Can any see what I'm doing wrong?

Thanks,
Joe


-----Original Message-----
From: Joe Farr [mailto:joe.farr@kcsl.uk.com] 
Sent: 09 January 2006 21:12
To: Joe Farr
Subject: RE: [PIC]: Embedinc's EasyProg and 18F4550

Thanks Olin,

http://www.embedinc.com/picprg/icsp.htm  

I'll make the changes you suggest and try again. 
Your web document is exactly what I was looking for.

I'll report back.

Thanks,
Joe




-----Original Message-----
From: Olin Lathrop [mailto:olin_piclist@embedinc.com] 
Sent: 09 January 2006 20:50
To: Joe Farr
Subject: Re: [PIC]: Embedinc's EasyProg and 18F4550

Joe Farr wrote:
> I've decided to start experimenting with the 18F4550 PIC but when
trying
> to program the PIC with ICSP I get a message from 'pic_prog' saying:
>
> "No information was found for a PIC with device ID word 2. This chip
is
> not supported."

This means communication isn't working quite right.  It appears to be
getting errors reading the device ID.

> Looking at the web site, the 4550 should be supported.

It is definitely supported.

One issue with that family of PICs is that the maximum Vpp voltage is a
bit
less than what the EasyProg normally puts out.  Back when the EasyProg
was
designed, all flash PICs had 13V in their valid Vpp range.  The family
of
PICs the 18F4550 belongs to have 12.5V maximum if I remember right.  I
have
noticed that it makes a difference.  I've seen these chips work at 12V
Vpp
but not at 13V.

You can try lowering resistor R8 to make a lower voltage for ICSP.  Note
that R8/R11 set the Vpp voltage for ICSP and 18 pin devices, and R9/R12
the
Vpp voltage for larger devices.

If you have DIP versions of these chips, try them in the ZIF socket
without
connection to the target circuit, although you will have to deal with
the
Vpp 13V issue first.

> I have the PIC on a plug-in bread-board.

Then it's best to get the programmer working on a bare PIC first, even
if it
is in a breadboard.  That way if it stops working later you know it has
something to do with the circuit.

> Both sets of PIC's power rails are connected, a 20MHz crystal and a
> couple of 20pf load caps.

How much capacitance is on the power rail?  A ceramic bypass cap is
fine,
but a large electrolytic is not.

> The MCLR pin is connected to +5v via a diode and a 10k resistor. This
> pin is also connected to the VPP pin on the programmer.

That sounds OK.

> PGD and PGC PIC pins are connected to the programmers Data and Clock
> pins respectively.

Try adding about 33-47pF caps to ground to these pins close to the
target
PIC.

> The PIC is being powered by it's own +5v supply from a 7805 regulator
-
> there are plenty of decoupling caps around.

That could be a problem.  The PIC should not be independently powered
during
programming.  The EasyProg expects to control Vdd.  Since this is on a
plug
in breadboard, try stripping things away until you are left with a bare
PIC,
the caps on PGC and PGD to ground, and either a resistor divider on Vpp
or a
modification of the EasyProg to produce a lower Vpp.  I would aim for
12V,
since that's still high enough for most other PICs.  I have one ProProg
around here I modified for 12V Vpp just to program this family of PICs.

> Voltage at the PIC is slightly over 5v.

Again, the programmer should be driving Vdd, not the target circuit.  It
will actually work with some PICs to power them anyway and not connect
Vdd
from the programmer, and I think these 18F parts are in this catagory,
but I
would first get things working as intended and then see what you can get
away with incrementally.

I have a writeup on ICSP at http://www.embedinc.com/picprpg/icsp.htm
that
you might want to look at.  It talks about designing the circuit to
allow
for ICSP.  You can't just easily add it on later.


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