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Troubleshooting Com Ports | Tech Info Home Page | Troubleshooting |


Com Ports

Serial devices like a mouse or a modem connect to a serial port (also known as a Com port). Com ports are located on the back of the computer. They can be either a 9-pin or a 25-pin Male connector and are normally assigned as com1 or com2.

Some computers have the serial ports taken up by components, such as a serial mouse or an internal modem.

A computer normally has 2 com ports with numbers ranging from Com1 to Com4. An internal modem will also count as a com port and with Plug-and-Play computers will be assigned the next available Com number.

You must be carefully with serial ports, the computer likes to have only a total of 2 Com ports, and since an internal modem counts as a Com port, a computer with 2 built-in Com ports and an internal modem can cause problems. Many companies disable one of the two internal Com ports to allow the modem to operate correctly. When this is done, you will still have the two physical ports on the back of the computer, but only one will operate correctly.

In almost all new computers, the Com ports are enabled or disabled using the BIOS setup which can only be accessed by pressing a key immediately after the computer is turned on.

When you connect the Label printer to a serial port you the following must be true.

On systems with 2 built-in com ports and an internal modem, the only safe com port you can use is one that is not an even or odd number as is the modem. So if your modem is com1 you cannot use com3, if its com2 you can not use com4.

Further, if your mouse is connected to a serial port it works as above with the modem. If the mouse is on com1 then using the com3 will cause problems, if its on com2 using the com4 will cause problems.

Com ports are one of the most frustrating devices on a computer.

Now, how to find out what ports are used on your computer.

1) Many systems briefly display a summary of the computer components when the computer is turned on. This includes the com/serial port assignments. The com ports will be be shown as "Com port : 3F8, 2F8". Each of the numbers (3F8, 2F8) counts as one com port. In this example there are two. So if you see Com Port: 3F8, 2E8, 2F8 that would be 3 com ports.

2) You can find out what com ports windows95 thinks it sees by going to

My Computer (on the desktop)
opening the Control Panel
opening the System icon, and pressing the Device Manager Tab.
You will then see the listing of the installed components.
You need to click on the + sign in front of "Ports (Com and LPT)"

You will then see the listing of the com ports that were detected by windows 95.

If any conflicts are detected by windows, the com port with the problem will have a "yellow exclamation point" in front of the entry. If this happens you will need to try to find where the conflict is and correct it.

IRQ settings

Typical settings for Com ports are:

 

 


 

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