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'PIC16C84 Bank mapping'
1999\04\22@121315 by Adam Chapweske

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Excuse me for asking this question, since this is something I should
already understand, but it just doesn't make any sense to me...

I was looking through Microchip's PIC16C84 datasheet and on page 12, the
second paragraph in section 4.2.1 reads:

"The GPR addresses in bank 1 are mapped to addresses in bank 0.  As an
example, addressing location 0Ch or 08h will access the same GPR."

Does this mean that when I write to 0Ch (the address of the first general
purpose register,) I'm actually writing to EEDATA (08h)?  Or is this just
an error and they meant 8Ch (instead of 08h)?  I'm assuming the latter,
but I'd like to make sure just in case.

Thanks,
Adam C.

1999\04\22@121946 by Tjaart van der Walt

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Adam Chapweske wrote:
>
> Excuse me for asking this question, since this is something I should
> already understand, but it just doesn't make any sense to me...
>
> I was looking through Microchip's PIC16C84 datasheet and on page 12, the
> second paragraph in section 4.2.1 reads:
>
> "The GPR addresses in bank 1 are mapped to addresses in bank 0.  As an
> example, addressing location 0Ch or 08h will access the same GPR."
>
> Does this mean that when I write to 0Ch (the address of the first general
> purpose register,) I'm actually writing to EEDATA (08h)?  Or is this just
> an error and they meant 8Ch (instead of 08h)?  I'm assuming the latter,
> but I'd like to make sure just in case.

It means that it is actually the same register that you can
access from different banks. 'Mapping' is just a fancy word
for it, I suppose...

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1999\04\22@155951 by Adam Chapweske

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I understand what mapping is...I guess what my question is is what is the
relationship between 0Ch and 08h?  Any diagrams I've looked at of the
memory organization have indicated that 0Ch and 08h are both in the same
bank (bank 0).  I've always thought that 0Ch should be mapped to 8Ch (its
bank 1 counterpart) and 08h should be mapped to 88h (again, its bank 1
counterpart.)  Boy am I confused!


On Thu, 22 Apr 1999, Tjaart van der Walt wrote:


{Quote hidden}

1999\04\22@163720 by Gerhard Fiedler

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At 14:58 04/22/99 -0500, Adam Chapweske wrote:
>I understand what mapping is...I guess what my question is is what is the
>relationship between 0Ch and 08h?  Any diagrams I've looked at of the
>memory organization have indicated that 0Ch and 08h are both in the same
>bank (bank 0).  I've always thought that 0Ch should be mapped to 8Ch (its
>bank 1 counterpart) and 08h should be mapped to 88h (again, its bank 1
>counterpart.)  Boy am I confused!

it's not so confusing... :) what they call GPR (general purpose registers)
are what usually is referred to as "ram"; this are the addresses from 0Ch
to 2Fh on the 16c84. when they say that "the addresses in bank 1 are mapped
to bank 0," it means that when you access 8Ch, it will actually access 0Ch
(their example with 08h is probably a typo, 08h isn't even a GPR). the
figure 4-2 to the right of the paragraph illustrates this. there are also
some "register files" which are mapped in both banks: indf, pcl, status,
fsr, pclath, intcon.

08h is eedata and 88h is eecon1, both are "register files" and not "gpr"s
-- and they are not mapped in both banks.

ge

1999\04\22@173710 by Nick Taylor

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Adam:
You are absolutely correct.  Addressing location 0Ch or 8Ch will
access the same register.  In the 16C84 registers 8Ch thru CFh are
mapped to locations 0Ch thru 4Fh.  Your data sheet must contain
a typo.  I have DS30445C and it does *not* contain the typo.
Have fun,
- - - Nick - - -

Adam Chapweske wrote:
{Quote hidden}

1999\04\23@005021 by Tjaart van der Walt

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Adam Chapweske wrote:
>
> I understand what mapping is...I guess what my question is is what is the
> relationship between 0Ch and 08h?  Any diagrams I've looked at of the
> memory organization have indicated that 0Ch and 08h are both in the same
> bank (bank 0).  I've always thought that 0Ch should be mapped to 8Ch (its
> bank 1 counterpart) and 08h should be mapped to 88h (again, its bank 1
> counterpart.)  Boy am I confused!

There is no relationship between 0Ch and 08h.
Read the datasheet again :

"  The GPR addresses in bank 1 are mapped to         "
"  addresses in bank 0. As an example, addressing    "
"  0Ch or 8Ch will access the same GPR.              "

0Ch and 8Ch map to the same register. (it *is* the
same register, in fact). This is true for all the
registers 0Ch - 2Fh, that map to 8Ch - AFh


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1999\04\23@175322 by Gerhard Fiedler

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At 07:02 04/23/99 +0200, Tjaart van der Walt wrote:
>Adam Chapweske wrote:
>> I understand what mapping is...I guess what my question is is what is the
>> relationship between 0Ch and 08h?  Any diagrams I've looked at of the
>
>There is no relationship between 0Ch and 08h.
>Read the datasheet again :
>
>"  The GPR addresses in bank 1 are mapped to         "
>"  addresses in bank 0. As an example, addressing    "
>"  0Ch or 8Ch will access the same GPR.              "

in my data sheet of the 16c84 (ds30445b, p.11-12), it actually says "As an
example, accessing location 0Ch or 08h will access the same GPR." which
seems to be a rather confusing typo. your citation makes more sense... :)

ge

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