Re: Using bitwise AND for setting configuration bits? What's all this about

"Tomás Ó hÉilidhe" <toe@xxxxxxxxxxx> wrote in message
news:eafe2d01-a21d-4f30-9a9d-563f96cfe6eb@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx


I've been programming the PIC16F684 for a few weeks now, and only
today did I notice the peculiarity of how the configuration bits were
being set:

__CONFIG(FCMDIS & IESODIS & BORDIS & UNPROTECT & MCLRDIS & PWRTEN &
WDTDIS & INTIO);

I would have expected bitwise OR to be used in conjunction with macros
that equate to an exact power of 2, like as follows:

#define FCMDIS 1
#define IESODIS 2
#define BORDIS 4
#define UNPROTECT 8
#define MCLRDIS 16
#define PWRTEN 32

__CONFIG(FCMDIS | IESODIS | BORDIS | UNPROTECT | MCLRDIS | PWRTEN |
WDTDIS | INITO);

Can anyone shed any light on their usage of bitwise AND for setting
config bits?


If you look at the definitions for the constants that are &'ed together you
will see that they define which bit should be cleared, not which bit should
be set. Hence the & rather than the |. I would hazard a guess it is done
this way for simplicity - to minimise the number of definitions you need to
change what would otherwise be the default behaviour.

--
Regards,
Richard.

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