Ed VanderPloeg wrote:
>
> At 08:00 AM 3/6/97 PST, you wrote:
> >Hi,
> >
> >I think I'm missing something very basic.  I'm using ByteCraft's MPC and
> >the target controller is the PIC16C74A.  This macro is supposed to take
> >2 unsigned 8-bit chars (h: high, l: low), concatenate them, and return
> >the unsigned 16 bit result.  Instead, it's masking (zeroing) the high
> >byte.
> >
> >#define WORD(h,l)   (((unsigned long)(h) << 8) | (unsigned char)(l))
> >
> >Thanks, Matt
> >
> I don't use the MPC compiler, but have you tried:
> - extra brackets around the first cast & the "(h)", like this:
> #define WORD(h,l)   ((((unsigned long)(h)) << 8) | (unsigned char)(l))
>
> - using a different cast like (uint16) or (word), to see if the compiler is
> only allowing 8 bits for the "long".
>
> - casting the whole macro to ensure a 16 bit output:
> #define WORD(h,l)   (unsigned long)(((unsigned long)(h) << 8) | \
>                                      (unsigned char)(l))
>
> IMHO, it seems there should be a much more efficient way to create a word
> out of two bytes than this.  I'm curious as heck what the compiler gives
> you for that macro.  Maybe it actually sets up a loop and shifts eight
> times (gross!).  Trouble is, I can't think of any alternatives right now.
> Anyone got ideas?
>
> -Ed V.

Ed,
As you can see, the compiler stores the high byte, clears the storage
location for the low byte, and ORs the low byte into the cleared
location.  The only inefficiency that I can see is the ORing into a
known-clear location (instead of a MOV).

BCF    STATUS,RP0    Sample = WORD(Phi, Plo);
MOVF   39,W
BSF    STATUS,RP0
MOVWF  46
CLRF   45
BCF    STATUS,RP0
MOVF   3A,W
BSF    STATUS,RP0
IORWF  45

BTW, the extra brackets didn't change the assembled code.  I still have
to try it in my target system.

Matt