;----------------------------------------------------------------------------------------;
;THIS PROGRAM IMPLEMENTS A CYCLIC BUFFER ON THE SERIAL PORT(RECEIVED DATA)               ;
;MEMORY POINTERS ARE STORED IN THE REGISTERS R0&R1(STARTING ADDRESS IS 20H)              ;
;BUFFER LENGTH IS 20H TO 30H LOCATION                                                    ;
;BUFFER SIZE CAN BE VARIED ACCORDING TO YOUR REQUIREMENT AND SIZE OF RAM                 ;
;----------------------------------------------------------------------------------------;
;This code is written by Mubashar Yasin(Islamabad,Pakistan).It is freely distributable   ;
;however please distribute it with my name and if you add this code to your website or   ;
;some other publication then mention about me along with this code.I have tested this    ;
;code to work properly even then there is no guarantee or warranty and i cannot be held  ; 
;responsible for any damage or loss due to this code.If you have any querries about this ; 
;code please contact me at:                                                              ;
;                                                                                        ;
;  kool_projects@yahoo.com                                                               ;
;  mubasharpk09@hotmail.com                                                              ;
;                                                                                        ;
;or visit my website:                                                                    ;
;                                                                                        ;
;  http://www.geocities.com/kool_projects                                                ;
;----------------------------------------------------------------------------------------;	
	
	
	
	START EQU 20H

	ORG 0000H
	LJMP MAIN

	ORG 0023H
        LJMP SERIAL_ISR
	
;;;;;;;;;;;;;;;;
SERIAL_INIT:
;;;;;;;;;;;;;;;;
        MOV SCON,#52H ;8-BIT UART,REN
        MOV TMOD,#20H ;8-BIT AUTO RELOAD MODE
        MOV TH1,#-3   ;9600 BPS AUTO RELOAD VALUE
        SETB EA       ;GLOBAL INTERRUPT ENABLE
        SETB ES       ;SERIAL INTERRUPT ENABLE
        SETB PS       ;HIGH PRIORITY FOR SERIAL INTERRUPTS
        SETB TR1      ;START TIMER
        RET
;;;;;;;;;;;;;;;;
SERIAL_ISR:
;;;;;;;;;;;;;;;;
	JNB RI,TMT
	CLR RI
	MOV A,SBUF
	LCALL C_BUFFER
	LJMP EXIT1
TMT:    CLR TI
EXIT1:	RETI
;;;;;;;;;;;;;;;;
C_BUFFER:
;;;;;;;;;;;;;;;;
	CJNE R0,#31H,NEXT1  ;CHECK FOR BUFFER RECYCLE 
	MOV R0,#20H         ;CYCLE AGAIN
NEXT1:	MOV @R0,A
	INC R0
	RET
;;;;;;;;;;;;;;;;
SERIAL_READ:
;;;;;;;;;;;;;;;;
	MOV A,R0
	MOV B,R1
	CJNE A,B,NEXT2       ;COMPARE R0 & R1
	LJMP EXIT2	     ;NOTHING TO READ(BUFFER EMPTY)
NEXT2:	CJNE R1,#31H,NEXT3
        MOV R1,#20H          ;JUMP TO START (RECYCLE)
NEXT3:	MOV A,@R1
        MOV R2,A
        INC R1
EXIT2:	RET
;;;;;;;;;;;;;;;;
MAIN:
;;;;;;;;;;;;;;;;
	MOV R0,#START        ;WRITE POINTER
	MOV R1,#START        ;READ POINTER
	LCALL SERIAL_INIT
AGAIN:	LCALL SERIAL_READ
	LJMP AGAIN
	END