Anyone remember which IRQs they use?
IIRC the ISA printers cards I have installed usually had jumpers to assign IRQ’s (range was usually IRQ 3-9). I don’t think there is any defined IRQ or memory address parameters for LPT 2/3, they simply have to have a usuable addresses defined (whatever they are) and the system will pick them up as additional printer port hardware.
It is also possible to share IRQs. In some situations I have installed printer cards with different memory address, both sharing IRQ 7. The only caveat is that you cannot send multiple jobs to both printers at the same time.
LPT1 used IRQ7.
LPT2 used IRQ5.
LPT3 was usually found on hercules graphics cards, and could usually be set to use either 5 or 7.
Very few printers used interrupts in the days of ISA cards.
It was common to assign the IRQs to something else, usually the sound card.