Lab3A.asm

 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 ;_____Control Word to Set Counter 0 to Rate Generator Mode
MODE3 EQU 36H	;_____Control Word to set Counter 1 to Square Wave Generator Mode
COUNT0	EQU 0008H	  ;counter0 address
COUNT1	EQU 000AH	  ;counter1 address
LOPT100uSEC		EQU 0F5H	   ;____Low Point for 100 uSec interval
HIPT100uSEC		EQU 00H		;____High Point for 100 uSec interval (counter decrements)
LOPT200uSEC		EQU 02H		;____Low Point for 200 uSec interval
HIPT200uSEC		EQU 00H		;____High Point for 200 uSec interval (counter decrements)

; 8259A Setup
CLR_A0      EQU 0000H		;Which CW's written here? ____Control register address where A0=0
SET_A0      EQU 0002H		;Which CW's written here? ____Control register address where A0=1
ICW1        EQU 17H		;____Edge Triggered, call interval of 4, single mode, ICW4 needed
ICW2        EQU 20H		;____Set Vector Address for IR0 to T5=1
ICW4        EQU 03H		;____Not special mode, Non-Buffered Mode, Auto EOI, 8086/8 Mode
OCW1        EQU 0FCH		;____Enable interrupts 0 and 1, mask rest

;-----------------------------------------------------------------------------
;       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
;___Counter 0 to generate square waves with a period of 100 uSec
;___Counter 1 to generate pulses with period of 200 uSec

            MOV DX,COUNT_CNTR   ;_____Set Counter 0 to mode 3: Square Wave Generator
            MOV AL,MODE3
            OUT DX,AL
            MOV DX,COUNT0
            MOV AL,LOPT100uSEC  ;_____Set counter 0 interval to 100 uSec
            OUT DX,AL
            MOV AL,HIPT100uSEC
            OUT DX,AL

            MOV DX,COUNT_CNTR   ;_____Set Counter 1 to mode 2: Rate Generator
            MOV AL,MODE2
            OUT DX,AL
            MOV DX,COUNT1
            MOV AL,LOPT200uSEC  ;_____Set counter 1 interval to 200 uSec
            OUT DX,AL
            MOV AL,HIPT200uSEC
            OUT DX,AL

; Initialize 8259A to : _____First ICW1 is used to set Edge Triggered mode,
; call interval of 4 and set to single mode, ICW4 needed. A0 = 0 at this
; point because we are doing ICW1. Then ICW2 is set (A0 = 1). ICW2 Sets the
; Vector Address for IR0 to T5=1 so we are using IR0 for interrupts.
; No ICW3 is used. ICW4 is used where its not special fully nested mode,
; Non-Buffered Mode, Auto EOI (End of interrupt) and obviously 8086/8 Mode.

            MOV DX,CLR_A0   ;_____Write ICW1 to the control register with A0=0
            MOV AL,ICW1
            OUT DX,AL
            MOV DX,SET_A0   ;_____Write ICW2 to the control register with A0=1
            MOV AL,ICW2
            OUT DX,AL
            MOV AL,ICW4     ;_____Write ICW4 to the control register with A0=1
            OUT DX,AL
            MOV AL,OCW1     ;_____Write OCW1 to the control register with A0=1
            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

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