NAME  		LAB3A

;*****************************************************************************
;		B E G I N N I N G    O F    P R O G R A M 
;*****************************************************************************

;-----------------------------------------------------------------------------
;		E Q U A T E S 
;-----------------------------------------------------------------------------

; 8255 Setup
CNTR_8255	EQU	0FFFEH		;Port control address
OUTPUT_MODE	EQU	0B5H		;Set up mode for port B output

; 8253 Setup
COUNT_CNTR	EQU	000EH		;counter control register address
MODE2		EQU	74H		;__________________________________
MODE3		EQU	36H		;__________________________________
COUNT0		EQU	0008H		;counter0 address
COUNT1		EQU	000AH		;counter1 address
LOPT1MSEC	EQU	0F5H		;__________________________________
HIPT1MSEC	EQU	00H		;__________________________________
LOPT2MSEC 	EQU	02H		;__________________________________
HIPT2MSEC	EQU	00H		;__________________________________

; 8259A Setup
CLR_A0		EQU	0000H		;ICW1,OCW2 written here
SET_A0		EQU	0002H		;other ICW's and OCW's written here
ICW1		EQU	17H		;__________________________________
ICW2		EQU	20H		;__________________________________
ICW4		EQU	03H		;__________________________________
OCW1		EQU	0FCH		;__________________________________

;-----------------------------------------------------------------------------
;		S T A R T    O F    V E C T O R    S E G M E N T 
;-----------------------------------------------------------------------------

VECTOR_SEG	SEGMENT
ORG		00080H			;Interrupt vector: type 32 dec.
		
IR0_IP_VECT	DW	?		;Low contains IP of ISR0
IR0_CS_VECT	DW	?		;High contains CS of ISR0
IR1_IP_VECT	DW	?		;Low contains IP of ISR1
IR1_CS_VECT	DW      ?		;High contains CS of ISR1

VECTOR_SEG	ENDS

;-----------------------------------------------------------------------------
;		S T A R T    O F    C O D E     S E G M E N T 
;-----------------------------------------------------------------------------

CODE_SEG        SEGMENT
ASSUME          CS:CODE_SEG, DS:DATA_SEG
ORG		00100H

;..............................................................................
;	PROCEDURE : INIT
;
;	- This procedure is called from the main program to initialize the 
;	  8253, the 8259A and the 8255.
;..............................................................................
INIT		PROC	NEAR
ASSUME		DS:DATA_SEG			;offset relative to data_seg

;Initialize the 8255 to set port B as output to DAC.

	 	MOV	DX,CNTR_8255    ; Port control address
		MOV	AL,OUTPUT_MODE  ; Set up mode for port B output
		OUT	DX,AL         

;Initialize 8253 counter0 and counter1 - counter2 is not used.
;Clock is the peripheral clock with frequency assumed to be 2.45MHz
;____________________________________________________________________________
;____________________________________________________________________________
;____________________________________________________________________________

		MOV	DX,COUNT_CNTR	;____________________________________
		MOV	AL,MODE3
		OUT	DX,AL
		MOV	DX,COUNT0
		MOV	AL,LOPT1MSEC	;____________________________________
		OUT	DX,AL
		MOV	AL,HIPT1MSEC
		OUT	DX,AL

		MOV	DX,COUNT_CNTR	;____________________________________
		MOV	AL,MODE2
		OUT	DX,AL
		MOV	DX,COUNT1
		MOV	AL,LOPT2MSEC	;____________________________________
		OUT	DX,AL
		MOV	AL,HIPT2MSEC
		OUT 	DX,AL

;Initialize 8259A to : _____________________________________________________
;___________________________________________________________________________
;___________________________________________________________________________
;___________________________________________________________________________
;___________________________________________________________________________

		MOV	DX,CLR_A0	;___________________________________
		MOV	AL,ICW1
		OUT	DX,AL
		MOV	DX,SET_A0	;___________________________________
		MOV	AL,ICW2
		OUT	DX,AL
		MOV	AL,ICW4		;___________________________________
		OUT	DX,AL
		MOV	AL,OCW1		;___________________________________
		OUT	DX,AL

;Initialization complete, interrupts still disabled.

		RET
INIT		ENDP

;..............................................................................
;	INTERRUPT SERVICE ROUTINE : ISR0
;..............................................................................
ISR0		PROC	NEAR
		IRET
ISR0		ENDP

;..............................................................................
;	INTERRUPT SERVICE ROUTINE : ISR1
;..............................................................................
ISR1		PROC	NEAR		
		IRET			
ISR1		ENDP

;..............................................................................
;	S T A R T     O F     M A I N     P R O G R A M 
;..............................................................................

ASSUME 		DS:VECTOR_SEG			;offset relative to vector_seg

;Set up the interrupt vectors.

BEG:		CLI				;Ensure no interrupt occurs.
 		MOV	AX,VECTOR_SEG		;DS = vector_seg
		MOV	DS,AX
		MOV	IR0_IP_VECT,OFFSET ISR0 ;load all ISR's IP and CS  
		MOV	IR1_IP_VECT,OFFSET ISR1
		MOV	AX,CS
		MOV	IR0_CS_VECT,AX
		MOV	IR1_CS_VECT,AX

ASSUME		DS:DATA_SEG			;offset relative to data_seg

                MOV     AX,DATA_SEG		;Define data segment
                MOV     DS,AX
		CALL	INIT			;Initialization
		STI				;Enable the interrupt now.
LOOP1:		
		JMP	LOOP1

CODE_SEG        ENDS

;----------------------------------------------------------------------------
;		S T A R T     O F     D A T A     S E G M E N T 
;----------------------------------------------------------------------------
DATA_SEG        SEGMENT

DAC_MEMORY	DB	0		;Store the current DAC value
GARBAGE		DB	0		;Store the garbage character.

DATA_SEG        ENDS

                END     BEG

;******************************************************************************
;	              E N D      O F      P R O G R A M
;******************************************************************************