;**********************************************************************
;   This file is a basic code template for assembly code generation   *
;   on the PIC16C64A. This file contains the basic code               *
;   building blocks to build upon.                                    *  
;                                                                     *
;   Refer to the MPASM User's Guide for additional information on     *
;   features of the assembler (Document DS33014).                     *
;                                                                     *
;   Refer to the respective PIC data sheet for additional             *
;   information on the instruction set.                               *
;                                                                     *
;                                                                     *
;**********************************************************************
;                                                                     *
;    Filename:    xxx.asm                                             *
;    Date:                                                            *
;    File Version:                                                    *
;                                                                     *
;    Author:                                                          *
;    Company:                                                         *
;                                                                     * 
;                                                                     *
;**********************************************************************
;                                                                     *
;    Files required: P16C64A.INC                                      *
;                                                                     *
;                                                                     *
;                                                                     *
;**********************************************************************
;                                                                     *
;    Notes:                                                           *
;                                                                     *
;                                                                     *
;                                                                     *
;                                                                     *
;**********************************************************************


         list      p=16c64a            ; list directive to define processor
         #include <p16c64a.inc>        ; processor specific variable definitions

         __CONFIG   _CP_OFF & _WDT_ON & _BODEN_ON & _PWRTE_ON & _RC_OSC

; '__CONFIG' directive is used to embed configuration data within .asm file.
; The lables following the directive are located in the respective .inc file.
; See respective data sheet for additional information on configuration word.

;***** VARIABLE DEFINITIONS
w_temp        EQU     0x20        ; variable used for context saving 
status_temp   EQU     0x21        ; variable used for context saving


;**********************************************************************

RESET_VECTOR    CODE    0x0000        ; processor reset vector
         clrf   PCLATH                ; ensure page bits are cleared
         goto   START                 ; go to beginning of program


ISR             CODE    0x0004        ; interrupt vector location

Interrupt:
        movwf   w_temp                ; save off current W register contents
        movf    STATUS,w              ; move status register into W register
        bcf     STATUS,RP0            ; ensure file register bank set to 0
        movwf   status_temp           ; save off contents of STATUS register
        bcf     STATUS,RP0            ; ensure file register bank set to 0

        ; Interrupt service routine goes here

        movf     status_temp,w        ; retrieve copy of STATUS register
        movwf    STATUS               ; restore pre-isr STATUS register contents
        swapf    w_temp,f
        swapf    w_temp,w             ; restore pre-isr W register contents
        retfie                        ; return from interrupt

MAIN_PROGRAM         CODE

START:

; remaining code goes here

        GOTO $

        END                       ; directive 'end of program'

