How can I tell which port in my PC is COM1 and which is COM2?

[s.garcia]

I performed a loopback test earlier and I found out that the DB-9 pin is COM1, but I can't figure out which of the other ports is COM2.

Help is much appreciated.

-Sergio

[Dennis_Knutson]

You want to physically identify a second serial port on your pc? First, verify in device manager or MAX that a second port is present. Then, look for another DB9 or DB25 with male pins. Try your loopback test on that.

[s.garcia]

The device manager on MAX does specify that there is a COM2 port enabled. This computer has only one DB9 pin male port, one DB25 pin female port, and a 15 pin port (8 pins top and 7 below). I tried the loopback test on the DB25 and 15 pin port, but it didn't work on either of them.

I have to communicate with a pressure controller through the 15 pins port (this is the one that interests me). If you could help me figure this out I would really apprecite it. Thanks.

-Sergio

[Dennis_Knutson · Accepted solution]

The 25 pin female is your printer port and the 15 pin is video. All of these should be documented in the pc's user manual. It's possible that Com2 is present on the motherboard but not connected to the back panel of the pc. You should be able to find documentation on the motherboard to see if this is true. All that you might need is an 8-pin ribbon cable with a header one one end and a DB9 on the other. Otherwise, a USB-RS232 converter is an inexpensive addition

[s.garcia]

Thanks Dennis. That's probably the case, I'll try that.

[JÞB]

---

s.garcia wrote:

I performed a loopback test earlier and I found out that the DB-9 pin is COM1, but I can't figure out which of the other ports is COM2.

Help is much appreciated.

-Sergio

---

Serg-

Assuming: you have a Windows OS (if not, kindly disregard.)

Windows reserves COM1 and COM2 for hardware that CAN be connected directly to the CPU.  That does not mean that your computer actually has the hardware for 2 COM ports.  In fact most desktop and laptop PC's only have 1 COM port installed (default is COM1).  Since the Hardware manager doesn't display a COM2 on your system, I would bet dollars against doughnuts that your system has only 1 of the 2 nativeCOM ports physically present.

If you need additional COM ports you will need additional hardware.  (BTW- when you install an expansion serial port(s) the lowest default address is COM3 even if there is no COM2)

[s.garcia]

Yes, this is the case. I opened the tower and the COM2 isn't connected to anything. The computer only has the COM1 and the LPT1 for the printer. Thanks for all your help everybody.