Write a program using three procedures. The first should read text from the keyb

Question

Write a program using three procedures.

The first should read text from the keyboard and store it in RAM.

The second should convert any upper case characters in the stored text to lower case.

The third should display the text on the VDU screen.

Modify the following for the above procedures:

; --------------------------------------------------------------
; A program to read in a string of text and store it in RAM.
; The end of text will be labelled with ASCII code zero/null.
; --------------------------------------------------------------
; THE MAIN PROGRAM
   MOV   BL,70   ; [70] is the address where the text will
           ; be stored. The procedure uses this.

   CALL   10   ; The procedure at [10] reads in text and
           ; places it starting from the address
           ; in BL.

           ; BL should still contain [70] here.

   CALL   40   ; This procedure does nothing until you
           ; write it. It should display the text.

   HALT       ; DON'T USE END HERE BY MISTAKE.
; --------------------------------------------------------------
; A PROCEDURE TO READ IN THE TEXT
   ORG   10   ; Code starts from address [10]

   PUSH   AL   ; Save AL onto the stack
   PUSH   BL   ; Save BL onto the stack
   PUSHF       ; Save the CPU flags onto the stack

Rep:
   IN   00   ; Input from port 00 (keyboard)
   CMP   AL,0D   ; Was key press the Enter key?
   JZ   Stop   ; If yes then jump to Stop
   MOV   [BL],AL   ; Copy keypress to RAM at position [BL]
   INC   BL   ; BL points to the next location.
   JMP   Rep   ; Jump back to get the next character

Stop:
   MOV   AL,0   ; This is the NULL end marker
   MOV   [BL],AL   ; Copy NULL character to this position.

   POPF       ; Restore flags from the stack
   POP   BL   ; Restore BL from the stack
   POP   AL   ; Restore AL from the stack

   RET       ; Return from the procedure.
; --------------------------------------------------------------
; A PROCEDURE TO DISPLAY TEXT ON THE SIMULATED SCREEN
   ORG   40   ; Code starts from address [10]
           ; **** YOU MUST FILL THIS GAP ****
   RET       ; At present this procedure does
           ; nothing other than return.

; --------------------------------------------------------------
   END       ; It is correct to use END at the end.

Explanation / Answer

;Main
MOV BL,70 ;
CALL 10 ;
CALL 100; 100 is in hex
CALL 40 ;
HALT ;

; PROCEDURE TO READ IN TEXT
ORG 10 ;
PUSH AL ;
PUSH BL ;
PUSHF ;

Rep:
IN 00 ;
CMP AL,0D ;
JZ Stop ;
MOV [BL],AL ;
INC BL ;
JMP Rep ;

Stop:
MOV AL,0 ;
MOV [BL],AL ;
POPF ;
POP BL ;
POP AL ;
RET ;
;till here already given in ques
; A PROCEDURE TO DISPLAY TEXT ON THE SIMULATED SCREEN
ORG 40 ;
PUSH AL ;save register
PUSH BL ;save register
PUSHF ;save register

Rep1:
MOV AL,[BL] ;get the character
CMP AL,0 ;check if it is null
JZ Stop1 ;
OUT 01 ;display on port 01 assuming VDU is on 01
INC BL ;increment BL
JMP Rep1 ;

Stop1:
POPF ;restore register
POP BL ;restore register
POP AL ;restore register
RET ;
; CONVERT UPPER CASE TO LOWER CASE
ORG 100 ;
PUSH AL ;save register
PUSH BL ;save register
PUSHF ;save register

Rep2:
MOV AL,[BL] ;get the character
CMP AL,0 ;check if it is null
JZ Stop2 ;
CMP AL,61 ;compare ascii value with 'a'
JNC Next ;if already a lowercase
ADD Al,20 ;convert to lower case by adding 32 i.e 20 in hex
MOV [BL],AL ;store it back
Next:
INC BL ;
JMP Rep2 ;

Stop2:
POPF ;restore register
POP BL ;restore register
POP AL ;restore register
RET ;
END;

here we have used the fact that ASCII value of lower case is 32 more than upper case character

Related Questions

Navigate

• Browse (All)
• Browse W
• Subjects

Integrity-first tutoring: explanations and feedback only — we do not complete graded work. Learn more.