--- title: "8086 ALP: convert text to uppercase" subject: "Microprocessor" chapter: 3 key: "semester_4/microprocessor:alp-8086-uppercase-text" source: https://www.bctengineer.com/q/semester_4/microprocessor/alp-8086-uppercase-text site: BCT Engineering --- # 8086 ALP: convert text to uppercase Microprocessor · Chapter 3: Programming with 8086 Microprocessor - Asked in: 2071 Bhadra, 8 marks - Video: [Convert lowercase to uppercase by assembly language](https://www.youtube.com/watch?v=Rrpz6TKZAcc) — Ahmed Khamis - Answer checked by Claude Opus 5.5 (high effort) on 2026-10-14 - Page: https://www.bctengineer.com/q/semester_4/microprocessor/alp-8086-uppercase-text - Whole chapter: https://www.bctengineer.com/md/semester_4/microprocessor/chapter-3 ## Question Write an assembly language program to read a text from keyboard, convert the text into uppercase and display on the cleared screen. ## Short answer Read the string with DOS function 0Ah. For each character in 'a' to 'z', clear bit 5 using AND 0DFH (subtract 20H). Replace the Enter code with '$', clear the screen, and display the converted string with function 09h. Example: Microprocessor 8086 becomes MICROPROCESSOR 8086. ## Answer **Method:** read the text with function 0Ah. Every lower-case letter ('a' to 'z') is converted to upper case by clearing bit 5 (`AND 0DFH`, i.e. subtracting 20H). Other characters are unchanged. The Enter code (0DH) at the end of the buffer is replaced by `$` so the whole string can be shown with function 09h after the screen is cleared. ```asm .MODEL SMALL .STACK 100H DISPSTR MACRO MSG ; display a '$'-terminated string LEA DX,MSG MOV AH,09H INT 21H ENDM CLRSCR MACRO ; clear screen and home the cursor MOV AX,0600H ; scroll whole window (AL=0 -> blank it) MOV BH,07H ; normal attribute MOV CX,0000H ; upper-left corner (row 0, col 0) MOV DX,184FH ; lower-right corner (row 24, col 79) INT 10H MOV AH,02H ; set cursor position MOV BH,00H ; page 0 MOV DX,0000H ; row 0, col 0 INT 10H ENDM .DATA MSG1 DB 'Enter text: $' BUF DB 80, ?, 80 DUP(0) ; DOS buffered-input area (max, actual, chars) CRLF DB 13,10,'$' .CODE MAIN PROC MOV AX,@DATA MOV DS,AX DISPSTR MSG1 ; prompt LEA DX,BUF ; read the string with DOS function 0Ah MOV AH,0AH INT 21H LEA SI,BUF+2 ; SI -> first character MOV CL,BUF+1 ; number of characters MOV CH,0 MOV BX,CX ; keep the length JCXZ SHOW CONV: MOV AL,[SI] CMP AL,'a' JB NEXT ; below 'a' CMP AL,'z' JA NEXT ; above 'z' AND AL,0DFH ; lower -> upper case MOV [SI],AL NEXT: INC SI LOOP CONV SHOW: MOV BYTE PTR [SI],'$' ; replace Enter by string terminator CLRSCR LEA DX,BUF+2 MOV AH,09H ; display converted text INT 21H MOV AH,4CH ; return to DOS INT 21H MAIN ENDP END MAIN ``` **Example:** `Microprocessor 8086` → `MICROPROCESSOR 8086`. ## Check yourself The answer's key points as multiple-choice questions, with the correct option and why. 1. How is a lower-case letter converted to upper case? A. OR with 20H B. AND with 0DFH (clear bit 5) C. ADD 20H D. XOR with 0FFH Answer: B. Clearing bit 5 is the same as subtracting 20H for letters a to z. (Key point: Conversion method) 2. Why are CMP with 'a' and 'z' done before AND 0DFH? A. To find the string length B. To count letters C. To make sure only lower-case letters are changed, leaving other characters intact D. To switch to signed arithmetic Answer: C. Applying AND 0DFH to digits or symbols could change them wrongly, so only 'a' to 'z' are converted. (Key point: Range check) 3. Why is the Enter code replaced with '$'? A. Function 09h displays a string only until a '$' B. Function 0Ah requires it C. The screen clearing needs it D. It converts the text to upper case Answer: A. INT 21h function 09h prints until it meets '$', so 0DH must be overwritten. (Key point: Terminator) 4. What is the output for Microprocessor 8086? A. microprocessor 8086 B. MICROPROCESSOR C. Microprocessor 8086 D. MICROPROCESSOR 8086 Answer: D. Letters become capitals and the digits stay unchanged. 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