Microchip has not revealed all the details about how ICD works.  Obviously
there is some hardware support for it, but ICD is mostly software.  That
means that it needs to be able to use mostly software tricks to read the
various registers.

If you think about it, there is no software way to look at the return stack.
If you look at the block diagram of the CPU, there is no path from the stack
registers or the stack pointer to the data bus.

So, the fact that the stack window is greyed out in ICD would imply that
whatever they added to the 16F8xx family to support ICD, they did not add
the extra hardware that would have been needed to display the stack.  I can
imagine those extra data paths being pretty messy to add.  I think it's
pretty cool that they added anything at all to the hardware to support ICD,
which is, after all, just there to support low-volume users.  So they made a
design compromise.  They sacrificed some silicon area in every single
production chip, but had to trade off how much silicon versus what ICD
features they got.

The fact that the ICE products do display a stack window implies that those
special ICE chips have an extra data path that somehow gives the emulator
access to these registers.

ICD is amazingly powerful for its very low cost, but obviously there are
compromises to make it so cheap.  If you are developing code professionally,
there is still justification for shelling out the extra $2K or so for the
full emulation.  The question is "Do you spend enough time debugging code to
justify the cost of the tool, (and does it make enough money to pay for
it)?"

> -----Original Message-----
> From: adastra [mailto:foster@ADASTRAN.COM]
> Sent: Thursday, October 05, 2000 7:35 PM
> To: PICLIST@MITVMA.MIT.EDU
> Subject: [PIC]: No stack window for '877 in ICD?
>
>
> I am using the MPLAB-ICD to program & debug an application
> using 16C877.
>
> I hadn't noticed until now that the stack window is "grayed
> out".  Can it be
> that it's not supported? Or do I just need someone smarter
> than me to tell
> me how to turn it on.  The documentation (onscreen and printed)when
> discussing "limitations", says only that one of the stack
> levels of the
> device is unavailable when using ICD.
>
> Having a new CALL / PCLATH problem, I'd sure like to see that stack.
>
> Thanks for any info anyone could provide.
>
>         Regards, Foster
>
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