XPS 8930, Dell single port serial card shows as 2 com ports

Question

Looking for suggestions as to why when a (new) single port serial card (534-BBBK) is installed in a (new) XPS 8930 with Windows 10, the port/COM that works is COM3 and not COM1.  To be clear, before attaching anything to the computer (after the card has been installed), the device manager shows 2 active ports:  COM1 and COM3.  COM1 is the communications port.  COM3 is labelled Pericom Serial Port.  COM1 ought to work as the serial port but it does not work when anything connected to it.  Instead COM3 works as the serial Port.  COM1 doesn't seem to work at all and COM3 seems to work instead.  Has anyone seen this before?  Why is It behaving in that manner?

RoHe · Accepted Answer

I have a Communications Port (COM1, serial.sys) on my XPS 8930 too. You can see more details about it by running msinfo32.exe from Start>Run. msinfo32 says It's using IRQ4 on my PC at 9600 baud.

Device Manager identifies it here as Physical Device: \device \00000034 and Hardware ID: PNP0501. You can read more about serial.sys here.

I don't know what motherboard device(s) is actually using COM1, but obviously something is using it. Your add-in card is working ok on COM3 so I'd be very careful about trying to re-assign the card to COM1 or trying to make the card use IRQ4.

If it ain't broke, don't break it!

Vic384 · Accepted Answer

@SteveXYZABC I was confused by the title of your post. The single port serial card only has one port. The card does not show 2 COM ports, the system is showing 2 COM ports, one on the motherboard and the other on the serial card. Generally, COM1 and COM3 use the same IRQ (IRQ4) by default. You can see the IRQs use by your system by going to Control Panel, Hardward and Sound, Device Manage, View, Resources by type, Interrupt request (IRQ). Although I do not recommend it, you can change the IRQ by going to the device driver for the serial card and in the Resources tab assign an unused IRQ for COM3. Usually this is done if there is a conflict.

savvy2 · Accepted Answer

the south bridge does NOT know, the port is not wired,  RS232 COM1 is not smart enough to know that, from 1980 it is there but dell did not wire it out   to DB9 JACK,  so it is there but not used,  on all PC mostly, now. the logic IS THERE, the Intel data sheet tells you this and the 4 IDs limits stated there too.  (note1 data sheet) PnP finds the logic and uses it. because it does not know the port is not wired on THIS motherboard. you do know this chip and vast other South bridges on 1000's of mobo may have a COm port actually wired. even in countries not  USA>  (yes, vast mobo exists, in the real world and configured vast ways, for sure) on some PC BIOS has  COM port disable. that might help but gee the card works now,  why worry port assignments, needlessly.>? Power on, F2 go to system configuration and serial ports, see?  (my 790 dell has that) mine are disabled.. by me. how dell uses com1 and 2, IDK but the logic is inside the SOUTHBRIDGE, for sure, all DELLS CALL and rules.. the Device mananger on mine clealy shows, South bridge, and yours will show series 300, if you looked.

savvy2 · Accepted Answer

well that is easy, all or most PC have a Com1 or 2, port(s) option in South Bridge,

some are vestigial and pre-Assigned (look in BIOS first see if com ports are there and turn those off)

if not in the Southbridge it is vestigial in the BIOS (reserved) ( for decades now) this.....

so the card or dongle installed, you simply look in DM device manager. see what you got.

lesson #2 any giving port, say yo see com1 there, click on properties then the tab DETAILS

the click , hardware ID's

see that ,? this...

eg ,mine: com1. (as you an see my z chip too , is reserved, A2C5 is the actual ID port address)

on Intel(R) 200 Series Chipset Family LPC Controller (Z270) - A2C5

ACPI\VEN_PNP&DEV_0501
ACPI\PNP0501
*PNP0501

for com ports wysiwyg, look and see that , also click view hidding in DM tab

now you know how to use the HARDWARE ID;'s to see what the hardware really is and made by whom.

why, is easy HISTORY LEGACAY hardware there or just the Echo of same, reserved,

gen8 Cpu, chipset Intel Z370

my z270 here show same vestage (the intel data sheet show this, but is unwired, for UART

the z370 page 274 shows how to program the south bridge UART.

"The UART 16550 8-bit Legacy mode only operates with PIO transactions. DMA transactions are not supported in this mode."

so it is there and is not wired to ports by dell ,best I know not wired (some PCs I have it is wired blank to header)

so just IGNORE that, install the card and let the PC assign COMx ports for you then set it up as you wish.

have many of these all work perfect (brands) and all never ever land on COM1 ever for above facts.

What is actually inside any south bridge is amazing and complex. check it out. search LEGACY there.

Vic384 · Answer

I am not sure if this helps, but I have a XPS 8910 and it shows a COM1 serial port in both Device Manager and HWINFO64 (a system information program). I am not aware of any serial port in this computer so I don't know why there is a driver installed. Perhaps you have the same situation and if a serial port card is installed there would be a conflict unless you adjust the IRQs the COM ports use.

speedstep · Answer

COM1 is  AMT HECI SOL  Intel(R) Active Management Technology Manageability Engine Serial Over LAN :

SteveXYZABC · Answer

Thanks for taking the time to reply.  The answer seems to be that Dell has pre-allocated COM1 in the system board, apparently as a legacy feature, and that the way going forward is simply use the COM number that Windows assigns they get put into use.  It seems to start at #3, COM3 and the numbers go up from there.  Thanks for the reply.

XPS Desktops

XPS 8930, Dell single port serial card shows as 2 com ports

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