 ;**********************************************************************
;   This file is a basic code template for object module code         *
;   generation on the PIC16F72. 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 and linker (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: P16F72.INC                                       *
;                                                                     *
;                                                                     *
;**********************************************************************
;                                                                     *
;    Notes:                                                           *
;                                                                     *
;                                                                     *
;                                                                     *
;                                                                     *
;**********************************************************************


    list        p=16f72        ; list directive to define processor
    #include    <p16f72.inc>    ; processor specific variable definitions
    
    __CONFIG   _CP_OFF & _WDTEN_OFF & _BODEN_OFF & _PWRTEN_ON & _RC_OSC

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

;***** VARIABLE DEFINITIONS (examples)

; example of using Uninitialized Data Section
INT_VAR        UDATA    0x20   
w_temp         RES     1        ; variable used for context saving 
status_temp    RES     1        ; variable used for context saving


; creating copies of interupt context saving variables in bank1
INT_VAR1       UDATA    0xA0
w_temp1        RES     1        ; variable used for context saving 


; example of using Uninitialized Data Section
TEMP_VAR       UDATA    0x22    ; explicit address specified is not required
temp_count     RES    1         ; temporary variable (example)

; example of using Overlayed Uninitialized Data Section
; in this example both variables are assigned the same GPR location by linker
G_DATA         UDATA_OVR        ; explicit address can be specified
flag           RES    2         ; temporary variable (shared locations - G_DATA)

G_DATA         UDATA_OVR   
count          RES    2         ; temporary variable (shared locations - G_DATA)

;**********************************************************************
RESET_VECTOR      CODE    0x0000      ; processor reset vector
    goto    start                     ; go to beginning of program

INT_VECTOR        CODE    0x0004      ; interrupt vector location

INTERRUPT

    movwf  w_temp          ; save off current W register contents
    bcf    STATUS,RP0      ; select bank0
    movf   STATUS,w        ; move status register into W register
    movwf  status_temp     ; save off contents of STATUS register

; isr code can go here or be located as a call subroutine elsewhere


    bcf    STATUS,RP0      ; select bank0
    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_PROG         CODE

start

    nop                    ; code starts here (example)
    banksel count          ; example
    clrf    count          ; example

; remaining code goes here

    goto $
    END                       ; directive 'end of program'

