Originally Posted by david_f_knight
04-16-2009 at 09:10:58 PM
I bought the Gigabyte LPT cable, 12CF1-1LP001-01R, directly from Gigabyte USA because I couldn't find any retailer in the United States that sells it. (I already had a GA-EP45-UD3R motherboard). I was disappointed with the cable I got. The quality is fine, but it's a generic cable, it's overpriced, and it's a hassle to order.
Gigabyte motherboards that have the LPT header have an unusual pinout. (Gigabyte provides the pinout on their website and in their user manuals.) The header is in a 2x13 configuration, which seems to be what is used on all motherboards that have LPT headers. Unfortunately, pin 24 rather than pin 26 in not connected, which is what makes Gigabyte LPT headers different. Pin 26 is connected to ground, but usually pin 24 would be connected to ground.
The DB-25 end of the LPT cable has 25 pins. Pins 18 - 25 should be connected to ground. If a straight ribbon cable is used to connect the LPT header (pins 1 - 25) to the DB-25 connector, then Gigabyte motherboards will leave DB-25 pin 25 unconnected (DB-25 pin 25 connects to LPT header pin 24).
Generic LPT port cables are available, and inexpensive. They use straight ribbon cables. They connect LPT header pins 1 - 25 to DB-25 connector pins 1 - 25 (but the pins are numbered differently).
Gigabyte has a LPT cable, part number 12CF1-1LP001-01R, but it is in fact just an overpriced generic cable. It uses a straight ribbon cable that does not compensate for the LPT header pin 24 vs. pin 26 issue.
If a circuit on a device connected to the DB-25 connector (via the Gigabyte LPT header and a generic cable) uses pin 25 for its ground connection alone, it will probably fail. If it ties at least one of the other DB-25 ground pins 18 - 24 to pin 25 (or doesn't use pin 25 at all) then it will probably work.
The Gigabyte LPT cable is not sold at many places, and they are overpriced and identical to the generic cables, which are cheaper and sold more places.
If you need a correct DB-25 LPT port from a Gigabyte motherboard, you could take a generic LPT cable, remove the ribbon cable from the IDC connector (it's not soldered), split the ribbon between wires 23 and 24, twist wires 24 and 25 180 degrees, and reinsert the ribbon cable into the IDC connector: wires 1 - 23 where they were before and wire 25 where it was before, but put wire 24 at the end (where the 26th wire of a 26 wire ribbon cable would go), leaving a gap where wire 24 was.
As far as using a USB to parallel port converter, or a PCI to parallel port converter, I don't recommend it. For one thing, the converters are much more expensive than a simple cable. For another, a USB or PCI converted parallel port cannot be configured the same as a true parallel port. The PC architecture devotes a specific set of I/O port addresses and interrupt channels to true parallel ports. USB and PCI do not use that same architecture. That's why a computer can operate all of them simultaneously without conflict. Software that requires a true parallel port will likely not work with a USB or PCI converted to a parallel port. I have read that some people have had a difficult time trying to install PCI to parallel port converters and were never able to make their external device work that was connected to the parallel port. (Also, I'm not sure that the voltages of the signals are the same for true parallel ports as compared to USB or PCI converted to a parallel port, either. True parallel ports use, I believe, +5V and ground for signals, but USB and PCI may use +3V and ground for signals, but I'm not sure about that.) Just because a plug fits into a socket doesn't mean that they're compatible. Some devices are more tolerant than others over such differences. Using a converter is a gamble.
By the way, you should be able to find a generic LPT cable (along with a COM cable!) for about $2 to $3, and if you buy it over the internet shipping should be about $2 to $3. Anything more and you're getting ripped off.
(Incidentally, Gigabyte uses the typical pinout for the COM port header. If you want both COM and LPT ports, Gigabyte only sells them as separate assemblies, requiring twice the space in your computer and twice the money. But you can get a single generic assembly with both, and for only about $3 to $4 total. That's what I would have gotten had I known beforehand that Gigabyte just sells generic cables.)