list		p=16f876A	; list directive to define processor
	#include	<p16f876A.inc>	; processor specific variable definitions
	
	__CONFIG _CP_OFF & _WDT_OFF & _BODEN_OFF & _PWRTE_ON & _HS_OSC & _WRT_OFF & _LVP_OFF & _CPD_OFF

; '__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	0x71		; variable used for context saving 
status_temp	EQU	0x72		; variable used for context saving
pclath_temp	EQU	0x73		; variable used for context saving			

indications EQU	0x74


;**********************************************************************
	ORG     0x000             ; processor reset vector
	nop			  		      ; nop required for icd
  	goto    main              ; go to beginning of program


	ORG     0x004             ; interrupt vector location
int
	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
	
	;RS232-Empfaenger-Interupt? 
    btfss   PIR1, RCIF 
    goto    intEnde          ; Interrupt came of where differently 
    movfw   RCREG            ; RS232-Register select 
    movwf   indications      ; and into the memory after 'indications' write 
write 
    movwf    PORTB         ; Indications at the PortB indicate 
     
    bcf      PIR1, RCIF     ; interrupt flag delete 


intEnde
	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

; remaining code goes here
	bcf		STATUS, RP0
	bcf		STATUS, RP1
	clrf	PORTB
	clrf	PORTA
	bsf		STATUS,RP0
	movlw	0x00
	movwf	TRISA
	movwf	TRISB
	
	call USART_initialize
	call USART_Baud_rate_adjust
	CALL prepare_Interrupts

	bcf		STATUS,RP0
	movlw	0xff
	movwf	PORTA

loop
	NOP
	goto loop


prepare_Interrupts				;Interrupts 
    BSF     STATUS, RP0         ; Bank1 
    BSF     PIE1, RCIE          ; Enable receive interrupts 
    BCF     STATUS, RP0         ; Bank 0 
    clrf    PIR1                ; all interrupt flags delete 
    clrf    PIR2 
    BSF     INTCON, GIE         ; generally permit interrupts 
    BSF     INTCON, PEIE        ; Interrupts of peripheral devices permit 
	RETURN

USART_initialize 
    BSF      STATUS, RP0       ; Bank1 
    MOVLW    0x24              ; Transmitter:RS232 , BRGH bit is set
    MOVWF    TXSTA             ; 
    BCF      STATUS, RP0       ; Bank 0 
    MOVLW    0x90              ; Enable serial port, 8bit reception , 
    MOVWF    RCSTA             ; continuous receive
	RETURN

USART_Baud_rate_adjust 
    BSF      STATUS, RP0    ; Bank1 
    MOVLW    0x81           ; Set Baud guesses 9,6 KB with Fosc=20MHz
    MOVWF    SPBRG  
	RETURN

	END                       ; directive 'end of program'