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Assembler/Linker/Librarian User’s Guide 4.68.6 Application Example - while/endw This example shows the usefulness of directive while to perform a loop while a certain condition is true. This directive is used with the endw directive. #include p16f877a.inc ;Include standard header file ;for the selected device. variable i ;Define the symbol 'i' as a ;variable. mydata udata 0x20 reg_hi res 1 reg_lo res 1 ;Allocate RAM for labels ;reg_hi and reg_lo. RST ;The code section named RST ;is placed at program memory ;location 0x0. The next two ;instructions are placed in ;code section RST. ;Jumps to the location labelled ;’start’. CODE pagesel goto start start shift_right i=0 while 0x0 macro i< by_n by_n ;Beginning of a macro, which ;shifts register data n times. ;Code length generated after ;assembly, varies depending upon ;the value of parameter 'by_n'. ;Initialize variable i. ;Following 3 lines of assembly ;code are repeated as long as ;i< by_n. Up to 100 lines of codes are allowed inside a while loop. bcf rrf rrf STATUS,C reg_hi,F reg_lo,F i+=1 ;Clear carry bit. ;reg_hi and reg_lo contains ;16-bit data which is rotated ;right through carry. ;Increment loop counter i. i cannot increment to more than 255 decimal. endw ;End while loop. The loop will ;break here after i=by_n. ;End of 'shift_right' macro. endm PGM CODE start movlw movwf movlw movwf DS33014L-page 166 0x88 reg_hi 0x44 reg_lo ;This is the beginning of the ;code section named PGM. It is ;a relocatable code section ;since no absolute address is ;given along with directive CODE. ;Initialize reg_hi and ;reg_lo for observation. 1994-2013 Microchip Technology Inc.
