Compile learning notes-mark register

Instance: converts lowercase letters in a string ending with 0 to uppercase letters.

Assume Cs: code, DS: datadata segment DB "Beginner's all-purpose Symbolic Instruction Code.", 0; double quotation marks ?? Data ends: converts lowercase letters in a string ending with 0 to uppercase letters. The parameter: DS: Si points to the first address of the string: code segment start: mov ax, data mov ds, ax mov Si, 0 call letterc mov ax, 4c00h int 21 hletterc: push ax; Register into Stack S: mov Al, [Si]; read characters CMP Al from memory, 0 je OK; if the value is 0, the child ends.ProgramCMP Al, 61 h jb next; if it is smaller than a, next CMP Al, 7ah ja next; if it is greater than Z, next sub Al, 20 h mov [Si], Al; reduce lowercase letters by 20 h and write them to memory in upper case: Next: Inc Si JMP short S; read the next character: OK: Pop ax; register the stack RET code endsend start