6.2.2 Character and String Conversions

A program can convert lowercase characters to uppercase by using Convert Character (Interrupt 21h Function 6520h), Convert String (Interrupt 21h Function 6521h), or Convert ASCIIZ String (Interrupt 21h Function 6522h). Using the uppercase conversion table associated with the current country and code page, Convert Character converts the character in the DL register, and Convert String and Convert ASCIIZ String replace each character in a string with its uppercase equivalent.

Although the case-conversion functions are available to all programs, it is often faster to carry out case conversions within the program itself.