The general-purpose bi-directional  parallel interface  is a 25-pin
connector on the back panel of the computer. This connector is generally
used for a parallel printer.

For each data byte written to the parallel port register, the hardware
automatically generates a pulse on the data ready pin.  The acknowledge
pulse from the parallel device is hooked up to an interrupt. For pin
connections and timing, see  Appendix E  and  Appendix F .