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'[PIC] Cloning 16F876(A) PICs'
2007\03\08@190349 by Tony Antoniou

picon face
Hi guys,

I've got a circuit which I'm hoping to duplicate to satisfy a project I'm
working on. Only problem is, since the code was developed for it, the
creator has left the mortal coil leaving me stuck. I could try to reinvent
the wheel but for simplicity's sake, I'm hoping I can just copy the hex out.

My question is though, the existing working PIC is a 16F876-20 and the only
PICs I can get my hands on now are 16F876A's. I realise the A version has
the 2 comparators thrown into it and the code protection works a little
differently, but since the existing code hasn't been protected (according to
the fuse configuration value at address 2007), would this hamper my attempt
to copy the hex directly across from the old IC to the new IC?


Adios,
Tony

2007\03\08@191841 by Jinx

face picon face
> 16F876A's. I realise the A version has the 2 comparators thrown into
> it and the code protection works a little differently

Are you sure ? I thought the A revision was programming specs (ie a
die revision), not functions. Assuming that's not the case, around the
start of the code you'd probably find a couple of instructions you could
substitute with a call to past the current program end, where you'd add
those replaced instructions and any extra set-up necessary



2007\03\08@195403 by Tony Antoniou

picon face
>From what I've noticed in Microchip's documentation, they have added the
comparators and the configuration code works out to be different for the
same settings. That is, for the 876, address 2007 has 3D72 whereas for the
same settings in the 876A, it must be 3F72. Other than that, it looks like I
can just copy it across as the additional registers used are in what were
probably reserved addresses in the older die, thereby not causing a
reshuffling of anything.

I've put it through a disassembler and the only thing it seems to have
changed is in the last portion which is the config.

876:
:02400E00723D01
:00000001FF

876A:
:02400E00723FFF
:00000001FF

Otherwise, the rest of the program code is identical.


Adios,
Tony

---------------  TAMA - The Strongest Name in Drums  ---------------

-----Original Message-----
From: spam_OUTpiclist-bouncesTakeThisOuTspammit.edu [.....piclist-bouncesKILLspamspam@spam@mit.edu] On Behalf Of
Jinx
Sent: Friday, 9 March 2007 11:18
To: Microcontroller discussion list - Public.
Subject: Re: [PIC] Cloning 16F876(A) PICs

Are you sure ? I thought the A revision was programming specs (ie a
die revision), not functions.

2007\03\08@203638 by Jinx

face picon face
> From what I've noticed in Microchip's documentation, they have
> added the comparators

> additional registers used are in what were probably reserved
> addresses in the older die

Yes, you're quite correct. My hard copy is DS30292B (87x) and
my drive copy is DS39582A (87xA). Register 9C is blank for the
87x and CMCON for the 87xA. I'd never had to use comparators
with the non-A but have with the A and hadn't noticed the difference.
Thanks for learning me one more bit of PIC info !!

2007\03\08@211113 by Tony Antoniou

picon face
Heheh. Pleasure. Hopefully, my theory holds true and just the configuration
hex is all that needs changing in the code I read out from the 876. The only
reason why I was so concerned is because even though the code protect bit
appears to be off, there's a gaping hole in the program code between
addresses 0D7h and 3A6h. The only thing that's sort of reassuring is that
0D7h finishes with a RETURN opcode and 3A7h starts with a CLRF of the STATUS
registers.

Oh well then, I'll bite the bullet and prototype a PCB for it. I'd
breadboard it, ordinarily, but I've got some old pre-coated boards which
probably won't react too well under UV anyway so I may as well make the most
of them now before they're completely useless. Fingers crossed on all
counts!


Adios,
Tony

---------------  TAMA - The Strongest Name in Drums  ---------------

{Original Message removed}

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