=

> ;
> ;       Configuration Bits
> ;                               IN MY BOOKS IT SAYS HERE
> =

>                                __CONFIG         H'3FF0'          ;SETS LP
> OSC, WDT OFF, PUT ON,
> =

> ;CODE PROTECTION DISABLED
> ;=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=
=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=
=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D
> =

> =

> =

> *********************************************************************
>                                         VELLEMAN / MICROCHIP THEN
> CONTINUES WITH
> =

> *********************************************************************
> =

> =

> _BODEN_ON                    EQU     H'3FFF'
> _BODEN_OFF                   EQU     H'3FBF'
> _CP_ALL                      EQU     H'03FF'
> _CP_75                       EQU     H'17FF'
> _CP_50                       EQU     H'2BFF'
> _CP_OFF                      EQU     H'3FFF'
> _DATA_CP_ON                  EQU     H'3EFF'
> _DATA_CP_OFF                 EQU     H'3FFF'
> _PWRTE_OFF                   EQU     H'3FFF'
> _PWRTE_ON                    EQU     H'3FF7'
> _WDT_ON                      EQU     H'3FFF'
> _WDT_OFF                     EQU     H'3FFB'
> _LVP_ON                      EQU     H'3FFF'
> _LVP_OFF                     EQU     H'3F7F'
> _MCLRE_ON                    EQU     H'3FFF'
> _MCLRE_OFF                   EQU     H'3FDF'
> _ER_OSC_CLKOUT               EQU     H'3FFF'
> _ER_OSC_NOCLKOUT             EQU     H'3FFE'
> _INTRC_OSC_CLKOUT            EQU     H'3FFD'
> _INTRC_OSC_NOCLKOUT          EQU     H'3FFC'
> _EXTCLK_OSC                  EQU     H'3FEF'
> _LP_OSC                      EQU     H'3FEC'
> _XT_OSC                      EQU     H'3FED'
> _HS_OSC                      EQU     H'3FEE'
> =

>         LIST
> =


To sum things up:

The configuration register is a location in program memory that configures =

different aspects of the chip. It has to be set during programming of the c=
hip =

and can't be changed by code running in the chip.

Different PICs have different configuration settings and to know which ones =

there are you need to read the datasheet. The configuration bits can set wh=
at =

type of oscillator circuit is used, if the watchdog timer is used or not, i=
f =

the brown out detector is used or not, if and how the chip is code protecte=
d =

and so on.

the __CONFIG directive tells the assembler that the word following is going=
 to =

be placed at the location for the configuration register. =


This word can be written as a constant in any radix (like H'3FF0') but then=
 you =

need to know which bits means what and build your word from that. In your c=
ode =

above, the programmer has done this and indicated with a comment what the =

configuration register with this value means. But this is kind of dangerous =

since you can change the configuration value without changing the comment.

To make things easier for the programmer and anybody that is going to read =
the =

source code, the include file for the different PIC processors contains a s=
et =

of macros that lets the programmer use more or less readable text (self =

commenting) to define the configuration word.

It has been chosen that the macros for the different configuration bits sho=
uld =

be ANDed together in order to make a complete configuration word. I'm not q=
uite =

sure why but doing like this automatically turns on any configuration bits =
that =

has its corresponding macro omitted in the __CONFIG directive.

As you can see in the include file, there are two or more macros for every =

different configuration function (which represents one or more bits in the =

configuration word) and all possible combinations for one configuration =

function can be selected using one of the macros for that configuration =

function. For example the macro _WDT_ON says that this is for the watchdog =

function and ON is one of the settings for this configuration function. Sin=
ce =

the watchdog only has one bit in the configuration register there are two =

macros for it - one for turning it on and one for turning it off.

To make sure you get the correct configuration word you pick ONE configurat=
ion =

setting macro for each configuration function from the include file and AND =

them together as the configuration word for the __CONFIG directive in the =

assembler file. So for the above include file you pick one of the macros fo=
r =

_BODEN, _CP, _DATA_CP, _PWRTE, _WDT, _LVP, _MCLRE, _ER_OSC, _INTRC_OSC and =
one =

of the four oscillator settings.

/Ruben


=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=
=3D=3D=3D=3D=3D
Ruben J=F6nsson
AB Liros Electronic
Box 9124, 200 39 Malm=F6, Sweden
TEL INT +46 40142078
FAX INT +46 40947388
ruben@pp.sbbs.se
=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=
=3D=3D=3D=3D=3D

-- =

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