; Timer interrupt  X-tal 11.0592 MHz AT89S8252 processor
;set serial receive for 19200/8/n/1

#include 8051.H
	.org	0000H
	sjmp	Main
	.org	0060H

Main	acall	Init
	mov	P1,	#0FH
run	inc	R1		; simple LED flash routine
	mov	P1,	R1
	mov	R4,	#255
	djnz	R4,	$
	mov	R4,	#255
	djnz	R4,	$
	sjmp	run
	.end


Init	mov	TMOD,	#21h 	; Timer 1 in Auto-reload mode, Timer 0 in 16 bit mode
	mov	TH1,	#253	; load T1 for 19200 baud
	
	mov	TH0,	#48h	; set for 20 ms
	mov	TL0,	#00	;
	
	mov 	IE,	#00h 	; reset intterupts
	mov 	PCON,	#80h	; set SMOD for 19200 baud
	mov	SCON,	#50h	; serial mode 1, REN=1
	setb	TR1		; start timer
	setb	TR0
	setb	EA		; enable interrups
	setb	ET0		; enable T0 
	mov	R1,	#00
	mov	P1,	#00
	mov	R3,	#250
	ret			; return

SEND	clr	TI		; Be sure the bit is initially clear
	mov	SBUF,	A	; send character
	jnb	TI,	$	; Pause until the TI bit is set. 
	ret			; return


;---------Interrupt Routines----------

	.org	000Bh		; T0 interrupt
	clr	TF0
	clr	TR0
	djnz	R3,	EXIT
	mov	TH0,	#48h	; set for 20 ms
	mov	TL0,	#00	;
	setb	TR0
	mov	A,	#'C'
	acall	SEND
	mov	R3,	#250	; for 5 sec interval
	reti
EXIT	mov	TH0,	#48h	; set for 20 ms
	mov	TL0,	#00	;
	setb	TR0

	reti