NAME            CLOCK
;**
;** 97.461 LAB 1, Part D.
;**
;** Runs an hour, minute, second clock on the SDK board display.
;**
CONTROL_REG     EQU     0FFEAH                  ;Set the address value
of the
DATA_REG        EQU     0FFE8H                  ; control and data port.

LED_ADDR        EQU     090H                    ;Set the starting of LED
addr.
MAX_SECONDS     EQU     60H
MAX_MINUTES     EQU     60H
MAX_HOURS       EQU     24H
ZERO            EQU     00H

;********* 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             100H

;** WAIT ** (Please write code below in space provided).
;**
;** Contains loops which run for approximately one second (within 25%).
;** Does not take into account the run time of the other procedures
;** in the CLOCK program (they are negligible with respect to the
;** processor speed variance).
;**
WAIT            PROC    NEAR









  RET
WAIT            ENDP

;** UPDATE **
;**
;** Increments the SECOND location modulo 60, then increments the MINUTE

;** location modulo 60 and the HOUR location modulo 24 if necessary.
;** Works in decimal arithmetic (note the decimal adjust operations that

;** are necessary).
;**
UPDATE          PROC    NEAR
  MOV     AL,SECOND
  INC     AL
  DAA
  CMP     AL,MAX_SECONDS
  JE      INC_MINUTES
  MOV     SECOND,AL
  RET
INC_MINUTES:    MOV     SECOND,ZERO
  MOV     AL,MINUTE
  INC     AL
  DAA
  CMP     AL,MAX_MINUTES
  JE      INC_HOURS
  MOV     MINUTE,AL
  RET
INC_HOURS:      MOV     MINUTE,ZERO
  MOV     AL,HOUR
  INC     AL
  DAA
  CMP     AL,MAX_HOURS
  JE      FINISHED
  MOV     HOUR,AL
  RET
FINISHED:       MOV     HOUR,ZERO
  RET
UPDATE          ENDP

;** WRITE **
;**
;** This subroutine writes the contents of the SECOND, MINUTE, and HOUR
;** locations to the SDK board display.  The 90H is written to the
control
;** register to initialize the display.  Data is written by
consecutively
;** writing the digits to the data register of the display, starting
from
;** the low digit of SECOND.  Each write increments the display address
;** automatically which was initialized to the rightmost digit.
;**
;** Before the output, the BCD digits are translated into 7-segment code

;** using the LED_TABLE.  The two digits of each field (SECOND, MINUTE,
;** HOUR) are separated before the translation.
;**
WRITE           PROC    NEAR
  MOV     AL,90H
  MOV     DX,CONTROL_REG
  OUT     DX,AL
  MOV     DX,DATA_REG
  LDS     BX,LED_TAB_PTR

  MOV     AL,SECOND
  AND     AL,0FH
  XLAT    LED_TABLE
  OUT     DX,AL
  MOV     AL,SECOND
  MOV     CL,4
  SHR     AL,CL
  XLAT    LED_TABLE
  OUT     DX,AL

  MOV     AL,MINUTE
  AND     AL,0FH
  XLAT    LED_TABLE
  OUT     DX,AL
  MOV     AL,MINUTE
  SHR     AL,CL
  XLAT    LED_TABLE
  OUT     DX,AL

  MOV     AL,HOUR
  AND     AL,0FH
  XLAT    LED_TABLE
  OUT     DX,AL
  MOV     AL,HOUR
  SHR     AL,CL
  XLAT    LED_TABLE
  OUT     DX,AL

  RET
WRITE           ENDP

;********* S T A R T     O F     M A I N     P R O G R A M *********
BEG:            MOV     AX,DATA_SEG             ;Set up the DS register
  MOV     DS,AX                   ;as ASSUMEd.
CONT:           CALL    WAIT                    ;Wait one second.
  CALL    UPDATE                  ;Update the time.
  CALL    WRITE                   ;Load to LED display.
  JMP     CONT                    ;Loop forever.

CODE_SEG        ENDS

;********* S T A R T     O F     D A T A     S E G M E N T *********
DATA_SEG        SEGMENT
ORG             200H

SECOND          DB      22H                     ;Storage for second
MINUTE          DB      59H                     ;Storage for minute
HOUR            DB      23H                     ;Storage for hour
LED_TAB_PTR     DD      LED_TABLE

;Translation table for 7-segment codes.
LED_TABLE       DB      3FH                     ; 0
  DB      06H                     ; 1
  DB      5BH                     ; 2
  DB      4FH                     ; 3
  DB      66H                     ; 4
  DB      6DH                     ; 5
  DB      7DH                     ; 6
  DB      07H                     ; 7
  DB      7FH                     ; 8
  DB      6FH                     ; 9

DATA_SEG        ENDS
  END     BEG