asm {
mov ah, 0x1
xor dx, dx
int 0x17
}


risultato in AH

BIT n=significato
7 1=Printer busy, 0=printer not busy
6 1=Acknowledge from printer
5 1=Out of paper signal
4 1=Printer selected
3 1=I/O error
2 Not used
1 Not used
0 Time out error

a te interessa il 7-imo bit,
quindi devi controllare che sia "0"