|
The contents of PCLATH and PCLATU are transferred to the program counter by any operation that writes to PCL. Similarly, the upper 2 bytes of the program counter are transferred to PCLATH and PCLATU by an operation that reads PCL. This is useful for computed offsets to the PC (see Section 5.1.6.1 “Computed GOTO”). The PC addresses bytes in the program memory. To prevent the PC from becoming misaligned with word instructions, the Least Significant bit (LSb) of PCL is fixed to a value of ‘0’. The PC increments by two to address sequential instructions in the program memory. The CALL, RCALL, GOTO and program branch instructions write to the program counter directly. For these instructions, the contents of PCLATH and PCLATU are not transferred to the program counter. ;****************************************************************************** ;Start of main program ; The main program code is placed here. ORG 0x1000 TABLE ;ADDWF PCL ;MOVWF PCL,F ADDWF PCL,F RETLW H'0F' RETLW H'0E' RETLW H'0D' RETLW H'0C' RETLW H'0B' RETLW H'0A' RETLW H'09' RETLW H'08' RETLW H'07' Main: MOVLW H'10' MOVWF PCLATH MOVLW D'4' CALL TABLE GOTO $ [img][/img]
|
楼主
发表于 2010-3-24 20:42
发表于 2010-3-27 10:18
