;**********************************************************************
;   This file is a basic code template for object module code         *
;   generation on the PIC16C925. 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: P16C925.INC                                      *
;                                                                     *
;                                                                     *
;                                                                     *
;**********************************************************************
;                                                                     *
;    Notes:                                                           *
;                                                                     *
;                                                                     *
;                                                                     *
;                                                                     *
;**********************************************************************


    list        p=16c925    ; list directive to define processor
    #include    <p16c925.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 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
pclath_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
        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
        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

        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'

