Hi WH Tan,

Microchip changed the PIC18F452.INC file at some point in time and dropped
several '16Cxxx/17Cxxx Substitutions' substitutions -- including CLRW.

The omissions were either intentional or an oversight. In any event, the
'Revision History' does not detail the omissions.
To see the details, compare the two PIC18F452.INC snippets below from the
latest MPLAB v6.41 installation and an older MPLAB installation.
There may have been other changes as well, but I'm just focusing here on
your original question about CLRW:




        PIC18F452.INC SNIPPET FROM MPLAB v6.41:


;==========================================================================
;
;       Revision History
;
;==========================================================================
;Rev:   Date:      Details:                                           Who:
;1.0    03/23/01   Modified C452 for F452                             tr
;1.1    08/01/01   Added EECON1 bits, corrected code protect config bit inserts
;1.2    09/17/01   Corrected MAXRAM,BADRAM                            tr
;1.3    10/23/01   Corrected CONFIG bits/registers                    tr/pas


;==========================================================================
;       16Cxxx/17Cxxx Substitutions
;==========================================================================

  #define clrw clrf WREG       ; PIC16Cxxx code substitution (WREG is
addressable)
  #define CLRW CLRF WREG       ; PIC16Cxxx code substitution (WREG is
addressable)
  #define negw negf WREG       ; PIC16Cxxx code substitution (WREG is
addressable)
  #define NEGW NEGF WREG       ; PIC16Cxxx code substitution (WREG is
addressable)
  #define movpf movff          ; PIC17Cxxx code substitution
  #define MOVPF MOVFF          ; PIC17Cxxx code substitution
  #define movfp movff          ; PIC17Cxxx code substitution
  #define MOVFP MOVFF          ; PIC17Cxxx code substitution
  #define lcall call           ; PIC17Cxxx code substitution
  #define LCALL CALL           ; PIC17Cxxx code substitution
  #define lgoto goto           ; PIC17Cxxx code substitution
  #define LGOTO GOTO           ; PIC17Cxxx code substitution
  #define DDRA  TRISA          ; PIC17Cxxx SFR substitution
  #define DDRB  TRISB          ; PIC17Cxxx SFR substitution
  #define DDRC  TRISC          ; PIC17Cxxx SFR substitution
  #define DDRD  TRISD          ; PIC17Cxxx SFR substitution
  #define DDRE  TRISE          ; PIC17Cxxx SFR substitution




        PIC18F452.INC SNIPPET FROM AN OLDER MPLAB INSTALLATION:


;==========================================================================
;
;       Revision History
;
;==========================================================================
;Rev:   Date:      Details:                                           Who:
;1.0    03/23/01   Modified C452 for F452                             tr
;1.1    08/01/01   Added EECON1 bits, corrected code protect config bit inserts
;1.2    09/17/01   Corrected MAXRAM,BADRAM                            tr
;1.3    10/23/01   Corrected CONFIG bits/registers                    tr/pas
;1.4    09/26/02   Include both names SWDTE and SWDTEN                pas


;==========================================================================
;       16Cxxx/17Cxxx Substitutions
;==========================================================================

  #define DDRA  TRISA          ; PIC17Cxxx SFR substitution
  #define DDRB  TRISB          ; PIC17Cxxx SFR substitution
  #define DDRC  TRISC          ; PIC17Cxxx SFR substitution
  #define DDRD  TRISD          ; PIC17Cxxx SFR substitution
  #define DDRE  TRISE          ; PIC17Cxxx SFR substitution

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