;**********************************************************************                                                                                                                                                                                                                                                                         ;**********************************************************************
;   This file is a basic code template for assembly code generation   *
;   on the PIC16C620. 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: P16C620.INC                                      *
;                                                                     *
;                                                                     *
;                                                                     *
;**********************************************************************
;                                                                     *
;    Notes:                                                           *
;                                                                     *
;                                                                     *
;                                                                     *
;                                                                     *
;**********************************************************************


    list      p=16c620           ; list directive to define processor
    #include <p16c620.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
        goto    start                     ; go to beginning of program

ISR     CODE     0x0004           ; interrupt vector location

interrupt:

    bcf     STATUS,IRP        ; initialize IRP bit state to 0
    btfsc   STATUS,RP0        ; test current state of bank 
    bsf     STATUS,IRP        ; set flag to indicate bank 1
    bcf     STATUS,RP0        ; ensure file register bank set to 0
    movwf   w_temp            ; save off current W register contents
    movf    STATUS,w          ; move status register into W register
    movwf   status_temp       ; save off contents of STATUS register
    
    
    bcf     STATUS,RP0        ; ensure file register bank set to 0
    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
    btfsc   STATUS,IRP        ; test for saved bank condition
    bsf     STATUS,RP0        ; restore file register bank information
    retfie                    ; return from interrupt

MAIN_PROG   CODE

start:

; remaining code goes here

        goto $

    END                      ; directive 'end of program'

