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Help....COM port in P55A ud4p

Last response: in Motherboards
March 13, 2010 6:08:07 PM

Since the P55A UD4P don't have a COM port i tried to Use a USB COM port ,And that didn't work , I also tried Buying
Another Non USB Com port, and connect it directly to the motherboard and that Also did not work , the computer did not Even see that com port . I tried cheking the bios and every thing .and i gave up .

Anyone who have any Ideas ?????

More about : port p55a ud4p

a c 177 V Motherboard
March 13, 2010 6:33:58 PM

I'm awfully confused??

Manual, page 7:

Manual, page 8:

Manual, page 11:

Manual, page 31:

Manual, page 52:
March 13, 2010 6:39:50 PM

That is true I've seen this manual , but when connect the com cable nothing happens even you can't see anything changes in the device manager , and that confuses me too
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a c 177 V Motherboard
March 13, 2010 7:08:37 PM

You should see this:

in your device manager, whether the port is hooked up to anything, or not - and it will not 'change' when it is hooked up...
If you are not seeing a port at all, it's either disabled in the BIOS, or you have some kind of BIOS/hardware problem. To actually connect something to it, you need the GB adapter (which seems impossible to get), or you need to 'hand-wire' a header and a DB-9 for it - there's a 'peculiarity' in the header pinout - when you are 'seeing' a port, I'll try to find the specifics for you - I did mine a long time ago, and can't seem to find where in the H I have saved it!! :pt1cable: 
March 13, 2010 7:13:53 PM

thanks for your help ,,, and your time
a c 177 V Motherboard
March 13, 2010 7:34:24 PM

Always welcome! ;)  Ahh - finally found the info I was thinking of - I had it stored under 'LPT pinout' as, indeed, the 'peculiarity' I noted is in the LPT port, not the COM port [:bilbat:3]
Just in case someone's looking:

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).

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.


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.)

I think it was from an old post at TweakTown, but so far as I know, they (GB) haven't changed anything in years!
March 13, 2010 7:44:59 PM

I will try that ASAP.

thanks for the help