mov ah, 34h ;Get InDOS Flag Address
int 21h
mov InDOS, byte ptr es:[bx] ;es:bx points to InDOS flag
Get InDOS Flag Address (Function 34h) returns the address of the MS-DOS InDOS flag. The InDOS flag shows the current state of Interrupt 21h processing.
This function has no parameters.
The ES:BX registers contain the InDOS flag address. The ES register contains the segment address of the InDOS flag, and the BX register contains the offset.
While MS-DOS is processing an Interrupt 21h function, the value of the InDOS flag is nonzero.