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PICList Thread
'[PIC]: On-Chip Debugging'
2001\07\17@192249 by parkiss

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Thanks to all who have pointed at Microchip's DS51242A, "PIC16F87X
Debugger Control".  I've studied that so hard for the last week I
can almost recite it from memory, and still have some fundamental
questions on how this works.  Here's the most mind-boggling:

The document states on page 10 describes how the debugger code gets
control:

 "As the processor vectors to 0x2004, the CPU will fetch and
 execute the instruction at this address. Therefore, address 2004
 must be programmed with a GOTO opcode, where opcode is pointing to
 the beginning address of the debug code."

I really can't wrap my head around this statement because it would
seem that the current contents of PCLATH would determine which page of
memory the GOTO statement would transfer to.  Is there some special
form of GOTO that must be used?

This is one of several questions pondered by Myke Predko, Bob
Ammerman, Tony Nixon, Dmitry Kiryashov, Olin Lathrop and Alejandro
Lavarello back in May of this year.  If answered, I can't find it in
the archives...

Any clues?  Thanks,

Steve

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2001\07\18@042233 by Bob Ammerman

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I think that the conclusion that we came to is that location 2004 should not
be programmed with a GOTO, but with the full actual address of the ICD
handler code. I forget they basis on which we came to this conclusion
however. Perhaps wishful thinking?

Bob Ammerman
RAm Systems
(contract development of high performance, high function, low-level
software)

{Original Message removed}

2001\07\18@182646 by Tony Nixon

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Bob Ammerman wrote:
>
> I think that the conclusion that we came to is that location 2004 should not
> be programmed with a GOTO, but with the full actual address of the ICD
> handler code. I forget they basis on which we came to this conclusion
> however. Perhaps wishful thinking?

Maybe(???) the data at 2004h is placed directly into the PC like a
return address off the stack. You don't need the PCLTAH then.


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Best regards

Tony

mICros
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2001\07\19@010208 by Bob Ammerman

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----- Original Message -----
From: "Tony Nixon" <.....Tony.NixonKILLspamspam@spam@ENG.MONASH.EDU.AU>
To: <PICLISTspamKILLspamMITVMA.MIT.EDU>
Sent: Wednesday, July 18, 2001 4:25 PM
Subject: Re: [PIC]: On-Chip Debugging


> Bob Ammerman wrote:
> >
> > I think that the conclusion that we came to is that location 2004 should
not
{Quote hidden}

Yeah, that's what I was saying.

Bob Ammerman
RAm Systems
(contract development of high performance, high function, low-level
software)

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2001\07\19@093940 by parkiss

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Thanks to Bob and Tony for the replies.  I'll stay after this until
the pain becomes too great and will share whatever new info develops.

Regards,

Steve

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