8086 ALP: convert text to uppercase

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.

.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.