If you look at the www.Lindsayengraving.com version, it shows transistor buffers, I have experimented with the TTL line driver encoders and scales, direct in to the port, seems to work better.
Note the other site link and the modern choices of Parallel port modes under Windows.
If buffers are needed, I prefer the 2N7000 Fet.
BTW DB9 is usually serial RS232?
Al.
CNC, Mechatronics Integration and Custom Machine Design
“Logic will get you from A to B. Imagination will take you everywhere.”
Albert E.