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'[PIC]:reading/writing 16F87x program memory'
2001\01\26@104750 by Mike Mansheim

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When reading/writing the 16F87x program memory from itself, can the
configuration word be accessed?
I'm looking at this with a 16F876 (on an emulator so I can watch
registers), using the "flash program read" code from the data sheet
verbatim.  I can read locations 0-1FFFh ok, but when I try to read 2007h,
EEADRH gets changed from 20h to 0.  I don't see any obvious bit in
EECON1 that might have something to do with this.
In the intro discussion of this section, the datasheet says "These devices
can have up to 8K words of program EEPROM with an address range from 0h to
3FFFh", which is the same address range mapped out in the programming
spec for this part - leading me to believe I would be able to access the
configuration word.
Thanks for any help.

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2001\01\26@114807 by M. Adam Davis

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Mike Mansheim wrote:
> When reading/writing the 16F87x program memory from itself, can the
> configuration word be accessed?

Nope.

{Quote hidden}

What you say is confusing.  If you are emulating an '876, then you have
the full 8k of programming memory, or, in other words, you should be able
to read 0x2007 just fine - it's within the program memory.  On this
particular chip the configuration word is outside this area, and you can't
go past 0x3fff.

-Adam

> Thanks for any help.
>
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2001\01\26@121039 by Darrel Johansen

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>When reading/writing the 16F87x program memory from itself, can the
>configuration word be accessed?
>I'm looking at this with a 16F876 (on an emulator so I can watch
>registers), using the "flash program read" code from the data sheet
>verbatim.  I can read locations 0-1FFFh ok, but when I try to read 2007h,
>EEADRH gets changed from 20h to 0.  I don't see any obvious bit in
>EECON1 that might have something to do with this.
>In the intro discussion of this section, the datasheet says "These
devices
>can have up to 8K words of program EEPROM with an address range from 0h
to
>3FFFh", which is the same address range mapped out in the programming
>spec for this part - leading me to believe I would be able to access the
>configuration word.
>Thanks for any help.

I don't know where you are seeing this 3FFF number,  there are 0x4000
bytes
of program memory, but they are addressed as 14-bit words from 0 to
0x1FFF.

The configuration bits cannot be read by your program in this part.  (The
18Cxxx
parts, however can read their config and ID bits.)  The config words at
200x
are just a convention for the tools to use.  When they see data at this
address
for the 16F87x devices, they put the chip into a special mode and program
the
config bits.

Program memory can be used for storage, but it doesn't have the same
capability
of R/W's that general purpose RAM storage has.  This parameter is called
"endurance," and for these flash parts starts to degrade at high temps (85

degrees C).  This is specified as absolute worst case, and so far we
haven't
seen MPLAB ICD's being reported as unprogrammable anymore, and we may
never see it.  I think that the worst case spec is something like a
thousand
reprogramming cycles before the odds are that one word will be
unprogrammable
at 85 degrees C operating.  Please consult the actual endurance specs for
your application.  My comments are for general information only and should
not be used for the purposes of establishing endurance values.

Darrel Johansen

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