© Thomas Kunz 2000
SCE 574
99
Subroutine Call/Return
äCALL does a push of
the instruction pointer (IP) onto the stack
automatically (FAR call also pushes segment information)
äRET pops the IP off
the stack automatically (If FAR call, the
FAR return is done automatically)
äConsider the
following nested subroutines
äPRINTB
prints 4 hexadecimal digits
PRINTB: MOV AL,BH ;get high order byte
CALL PBYTE ;print both nibbles
MOV AL,BL ;get low order byte
CALL PBYTE ; print both nibbles
RET
PBYTE: PUSH AX ;saves a copy of value AX
MOV CL,4 ;shift AL right 4 bits
SHR AL,CL
CALL PRINT ;print hex digit low nibble
;of
AL
POP AX ;restore value of AX
CALL PRINT ;print second hex digit
RET
Always push
words not
bytes
