Bueno, te dejo esto para probar esta interrupcion que te devuelve el estado del puerto paralelo:
http://www.ctyme.com/intr/rb-2100.htm
Y aca esta la tabla que figura ahi:
Bitfields for printer status:
; Bit(s) Description (Table 00631)
; 7 not busy
; 6 acknowledge
; 5 out of paper
; 4 selected
; 3 I/O error
; 2-1 unused
; 0 timeout
; Notes: If both, bit 5 "out of paper" and 4 "selected" are set, the
; MS-DOS/ PC DOS kernel assumes that no printer is attached.
; for Tandy 2000, bit 7 indicates printer-busy when set rather than clear
Experimenta un poco, deberia servirte
