;aruna and mazhalai
;4 dec 99
;uart prog for 8515 ver1...and it worked!!!
;prog recieves a data and outputs it to port B and echoes it 
;back by incrementing the same
;transmission and reception is done at 9600 bps

.include"..\..\8515def.inc"

.def rtemp=r17  	;temporary register
.def rreg=r18		;register for recieving data
.def treg=r19		;register for transmitting

.equ baudrate=$33 	;baud rate of 9600 bps for a clock frequency of 8 Mhz
.equ RXC=7		;UART recieve complete flag( 7th bit of USR register)
.equ UDRE=5		;UART data register empty flag(5th bit of USR register)

.cseg
.org 0
	rjmp RESET	;reset handle
	rjmp RESET
	rjmp RESET

RESET: 	ldi r16, low(RAMEND)	;initialising stack
	out SPL,r16

	ldi r16,HIGH(RAMEND)	
	out SPH,r16

	ldi r16,255  		;initialising port B for output
	out DDRB,r16
	
	rcall init_uart		;initialising 8515 for transmit and recieve
	
up:	rcall rxcomp		;recieving data

	out portb,rreg		;outputting data at port B

	inc rreg		;incrementing recieved data
	mov treg, rreg

	rcall txcomp		;transmitting data

 	rjmp up

;subroutine for initialising baudrate and UART control register
	
init_uart:
        ldi rtemp, baudrate     ;setting baud rate 
        out UBRR,rtemp
        ldi rtemp, $18		;initialising UART control register
        out UCR, rtemp
        ret

;subroutine for recieving data

rxcomp: sbis USR,RXC      	;poll to check if char received
        rjmp rxcomp
        in rreg,UDR     	;put received data in rreg
        ret

;subroutine for transmitting data

txcomp: sbis USR,UDRE      	;poll to check end of transmission
        rjmp txcomp
        out UDR, treg
        ret