;**********************************************************************
;   This file is a basic code template for object module code         *
;   generation on the PIC16C771. 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: P16C771.INC                                      *
;                                                                     *
;                                                                     *
;                                                                     *
;**********************************************************************
;                                                                     *
;    Notes:                                                           *
;                                                                     *
;                                                                     *
;                                                                     *
;                                                                     *
;**********************************************************************


    list      p=16c771            ; list directive to define processor
    #include <p16c771.inc>        ; processor specific variable definitions
    
    __CONFIG   _CP_OFF & _WDT_ON & _BODEN_ON & _PWRTE_ON & _VBOR_25 & _ER_OSC_CLKOUT
; '__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 Shared Uninitialized Data Section
INT_VAR       UDATA_SHR   
w_temp        RES     1           ; variable used for context saving 
status_temp   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
    movwf   status_temp       ; save off contents of STATUS register

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

    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'

