To further muddy this up....

I like to use CBLOCKs to allocate 'enum' style names. A primary example of 
this is bit positions in a flags byte:


FLAGS    RES    1

    CBLOCK    0
        FLAG_Happy
        FLAG_Dopey
        FLAG_Doc
        FLAG_Sleepy
    ENDC

or command codes:

    CBLOCK    CMD_Start
       CMD_COPY
       CMD_FETCH
       CMD_STORE

       CMD_End        ; Dummy endmark
    ENDC

CMD_Count = CMD_End - CMD_Min


Bob Ammerman
RAm Systems



----- Original Message ----- 
From: "Olin Lathrop" <olin_piclist@embedinc.com>
To: "Microcontroller discussion list - Public." <piclist@mit.edu>
Sent: Monday, January 24, 2005 6:26 PM
Subject: Re: [PIC] Equates or CBlock?


> Andrew Warren wrote:
>>     I guess... But as long as EQU and CBLOCK can be used in a
>>     program that also uses RES, the block isn't really "allocated";
>>     it's just protected from reuse by other RES directives, in the
>>     same way that registers named using CBLOCK can be kept from
>>     being renamed by other CBLOCK directives.
>
> The RAM is truly allocated by the linker, and that only happens when you 
> use
> RES.  Of course there is nothing preventing you from creating a symbol 
> that
> happens to have the value of a RAM address, but that has nothing to do 
> with
> allocating the RAM.  This is the distinction between RES on one hand, and
> CBLOCK and EQU on the other.  The only reason there is any confusion is
> because valid RAM addresses also happen to be integer values that can have
> other meanings.
>
> For example, the assembler can't prevent you from doing something 
> boneheaded
> like:
>
>  bkcnt  equ  h'20'    ;number of buckets left to fill
>
> because there is no way to tell this inappropriate useage from an
> appropriate one such as:
>
>  buckets equ h'20'    ;number of buckets in each tray
>
> And by the way, one CBLOCK statement does not prevent other CBLOCK
> statements from assigning the same values to different symbols.  Each 
> CBLOCK
> merely assigns sequential values to a list of symbols.  It has absolutely
> nothing to do with RAM allocation.
>
>>     This is in contrast to what I think of as "real" allocation...
>>     Which would be the sort of thing you see in high-level
>>     languages, where (generally speaking) once a variable name is
>>     declared/used, other variable names will never be assigned to
>>     the same RAM.
>
> But that is exactly what RES does.  It is not possible to RES the same
> memory location twice.
>
>
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