mov cx, StringLength ;length of string in bytes
mov dx, seg String
mov ds, dx
mov dx, offset String ;ds:dx points to string to convert
mov ax, 6521h ;Convert String
int 21h
jc error_handler ;carry set means error
Convert String (Function 6521h) converts each character in the specified string to an uppercase character using the current uppercase table.
StringLength
Specifies the length of the string in bytes.
String
Points to the string to convert.
The function replaces the original characters in the string with the corresponding uppercase characters (if any).
Function 6520h Convert Character
Function 6522h Convert ASCIIZ String