If the title of this post rings a bell with you, then you probably have a rather old CNC router or other similar device. If you’re like me, you tried to use a USB to DB25 adapter to hook up to your CNC’s parallel port input to no avail (even though you’d read it wouldn’t work), then finally settled for a rather old PC with this ancient peripheral built-in.
Personally, I find it a bit annoying that these ports are very hard to come by, since many engineers and tinkerers are only able to outfit home labs with perfectly functional legacy equipment. On the other hand, the vast majority of people don’t need to interface with older equipment, so I suppose its rarity is understandable.
Rant aside, there is at least a solution to your older CNC problem; you can use an Arduino with GRBL for control. If you’d rather not rewire everything, this kit, available on Tindie will let you simply send your GCODE to an Arduino, then it can send signals through a parallel port on a shield. According to the description, this leads to smoother timing, but it seems to me the real advantage is in not having to worry about finding an appropriate computer (or PCI parallel port) to run it!
You can see this Arduino/Parallel port CNC setup in the video below, and this shows it running off of an actual parallel port if you’d like to compare. Note that you’ll need to supply your own Arduino UNO and a female to female parallel cable to get things working.