;**********************************************************************
;   This file is a basic code template for object module code         *
;   generation on the PIC16F74. 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: P16F74.INC                                       *
;                                                                     *
;                                                                     *
;                                                                     *
;**********************************************************************
;                                                                     *
;    Notes:                                                           *
;                                                                     *
;                                                                     *
;                                                                     *
;                                                                     *
;**********************************************************************

    
    list        p=16f74        ; list directive to define processor
    #include    <p16f74.inc>   ; processor specific variable definitions
    
    __CONFIG   _CP_OFF & _WDT_OFF & _BODEN_OFF & _PWRTE_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    0x70   
w_temp         RES     1        ; variable used for context saving 
status_temp    RES     1        ; variable used for context saving
pclath_temp    RES     1        ; variable used for context saving


; creating copies of interupt context saving variables in bank1
INT_VAR1       UDATA   0xF0
w_temp1        RES     1        ; variable used for context saving 


; example of using Uninitialized Data Section
TEMP_VAR      UDATA    0x20     ; 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
    pagesel start
    goto    start                 ; go to beginning of program


INT_VECTOR        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             ; select bank0
    movwf  status_temp            ; save off contents of STATUS register
    movf   PCLATH,w               ; move pclath register into w register
    movwf  pclath_temp            ; save off contents of PCLATH register

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


    bcf    STATUS,RP0             ; select bank0
    movf   pclath_temp,w          ; retrieve copy of PCLATH register
    movwf  PCLATH                 ; restore pre-isr PCLATH register contents
    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'