1. A communications resource is a physical or logical device that provides a single, asynchronous data stream. Communications ports, printer ports, and modems are examples of communications resources. Two types of communications resources appear as ports in Device Manager:
a. Communications ports: These ports, also called COM ports, serial ports, or RS-232 COM ports, connect RS-232- compatible serial devices, such as modems and pointing devices, to the computer. Several types of communications ports might be listed in Device Manager:
b. Serial ports: Ports -- also known as RS-232 COM ports, to which external serial devices can be attached. Typically these ports require a 9- or 25-pin plug. Serial ports designed for Windows use the 16550A buffered UART which has a 16-byte FIFO that gives the CPU more time to serve other processes and that can serve multiple characters in a single interrupt routine.
c. Internal modem adapters: Internal modems are modems that are constructed on an expansion card to be installed in an expansion slot inside a computer.
Note: When installing a communications device, Windows assigns COM names to communication ports, internal modem adapters, and PC Card modem cards according to their base I/O port addresses as shown in the following list. Please also note that if a device has a nonstandard base address or if all four standard ports are assigned to devices, Windows assigns the modem to COM5 or higher. Some 16-bit version 3.1-based applications might not be able to access ports higher than COM4. Thus, when using the System option in Control Panel, you must adjust the base address in Device Manager or delete other devices to free a COM port at a lower address.
COM1 at address 3F8
COM2 at address 2F8
COM3 at address 3E8
COM4 at address 2E8
d. Printer ports: These ports, also known as LPT ports or parallel ports, connect parallel devices, such as printers, to the computer..
Note: If Windows does not detect an internal modem, the modem must be installed and configured by using the Modems option in Control Panel.
2. If an analog or ISDN modem is not on the Windows Hardware Compatibility List (HCL) or is not detected by the Add Hardware Wizard, use one of the following procedures to install it:
a. Check the modem. If it is an external modem, make sure it is turned on and all cables are tightly connected. If the modem is internal, verify that it is properly installed.
Note: If the modem is a Plug and Play device, open Device Manager in Control Panel and select Scan for hardware changes on the Action menu to reinstall the modem. To open Device Manager, open Control Panel and then double-click System. Click the Hardware tab, and then click Device Manager. If the modem is not a Plug and Play device, reinstall the modem using Add Hardware.
b. Obtain an .inf (installation) file from the modem manufacturer specifically for the version of Windows used. Follow the manufacturer's instructions for installing the modem, or contact the modem manufacturer for assistance.
c. Install your modem as a standard modem by using the Add Hardware Wizard. This option provides basic dialing and connectivity support for the modem, although manufacturer-specific features might be unavailable.
3. Application cannot dial selected modem:
a. If you cannot use an application to dial your modem, test the modem to verify that Windows can connect to it. In the Phone and Modem Options dialog box, select the Modems tab, click Properties for the modem you want, and then select the Diagnostics tab. Click Query Modem to send a set of AT commands to the modem. If the modem response is not displayed in the Response area, then perform the following steps to diagnose the problem:
(1) If an external modem is experiencing problems, make sure that the serial cable connection between the computer and the modem is secure and that the cable is not broken or frayed.
(2) Verify that Windows recognizes COM ports by displaying Device Manager. Verify that the COM port is not experiencing a hardware or resource problem (identified by an exclamation point icon next to the device listing) or has been disabled (identified by the international "No" symbol). If the connected port is listed without any additional icons, the COM port is recognized and available.
b. If the COM port is disabled in Device Manager, a hardware or a configuration problem is likely. Use the following steps to troubleshoot the problem for an external modem:
(1) Verify that the port is not disabled in the BIOS (also called the CMOS) setup of the computer. Refer to the documentation for your computer to obtain information about configuring options in the BIOS setup.
(2) Make sure there are no other adapters or devices that are configured for the same base I/O address or interrupt request (IRQ) as the COM port to which the modem is attached.
(3) Verify that the serial port is not defective. If the modem and any other serial devices fail on the COM port but work on other COM ports, and you have verified the two steps above, the serial port might be defective.
c. If the modem experiencing problems is internal, perform the following steps to diagnose and resolve the problem:
(1) If the internal modem is not Plug and Play-compatible, it might use jumpers to specify the COM port. Make sure the jumpers on the modem are configured properly. There might or might not be jumpers that allow you to set the base I/O address and IRQ to be used by the modem as well. Verify that they are properly set. Some modems use a configuration application to change these settings.
(2) If the modem is configured for a COM port number that is assigned to a COM port on the motherboard or a serial card (physical port), you must either set the modem to use a different COM port, or use the BIOS setup to disable the COM port that has the same number as the internal modem.
(3) Make sure that no other adapters or devices are configured for the same base I/O address or IRQ as the internal modem.
(4) Verify that the internal modem is not defective. Also, check with the vendor of your modem to see if there is an upgrade available for your modem.
4. The very first thing before installing a modem, is to ensure that any and all modem information on a system is removed first (uninstalled).
a. When you install a Plug and Play modem, Windows automatically configures the device so it will work properly with the other devices installed. As part of that configuration process, Windows assigns a unique set of system resources to all devices and these resources can include one or more of the following. Also note that each resource assigned to a device must be unique to itself and no other, or one or more of the devices will simply not function. For Plug and Play devices, Windows automatically ensures that these resources are configured properly.
Interrupt request (IRQ) line numbers
Direct memory access (DMA) channels
Input/output (I/O) port addresses
Memory address ranges
b. Occasionally, two devices require the same resources resulting in a device conflict. If this occurs, manually change the resource settings to be sure each device is unique. Some resources such as interrupts on PCI devices can be shared however -- depending on the drivers and computer. Please access and read, "Device Manager."
c. When you install a non-Plug and Play device, the resource settings for the device are not automatically configured. Depending on the type of device installed, you may have to manually configure these settings. Instructions for doing so should be supplied in the manual.
d. Generally, resource settings should not be done manually, because when you do, these settings become fixed, and Windows will then have less flexibility when allocating resources to other devices. If too many resources become fixed, Windows may not be able to install new Plug and Play devices.
e. To manually configure devices, use the device Propertiesdialog in Device Manager.
Warning: Changing resource settings improperly can disable your hardware and cause your computer to malfunction or become inoperable. Resource settings should only be changed if you are certain the new settings do not conflict with other hardware, or if a hardware manufacturer has provided you with specific resource settings for a device.
5. To install modem hardware, it is recommended that you refer to the manufacturer's documentation. Generally, the following instructions apply:
a. For internal modems with jumpers, set the jumpers for Plug and Play or as instructed in the documentation.
b. Make sure that it is seated in the proper slot on the mother board.
c. If it is an external, make sure it is plugged into the power source and turned on before turning on the computer.
d. Connect either type modem to a usable phone line with the proper connector -- paying attention to whether there is a Line or Phone jack on the back of the modem.
6. To install a modem, you must be logged on as an administrator or a member of the Administrators group.
a. Open the Phone and Modem Options in Control Panel (Click Start, Control Panel, Network and Internet Connections), and if you are prompted for location information, specify the dialing information for your location, and then click OK.
b. On the Modems tab, click Add and follow the instructions in the Install New Modem Wizard and let Windows automatically detect the modem -- generally recommended if Windows has compatible drivers.
c. In the Install New Modem Wizard, select the Don't detect my modem; I will select it from a list check box, and then click Next.
d. Do one of the following:
(1) If a modem is listed, that is a good match. Select it from this list by clicking the manufacturer and model, and then click Next.
(2) If the modem is not listed, and you have an installation disk or .inf file provided by the manufacturer, click Have Disk and specify the proper path. Follow instruction in the Install New Modem Wizard.
Note: Whenever possible, get the latest installation disk or modem .inf file designed for Windows from the manufacturer. This can usually be downloaded from their Web pages. If no installation file is available for a modem, the manufacturer's instructions that came with the modem may specify a compatible modem. Otherwise, click (Standard Modem Types) in the Manufacturers applet, and try choosing the standard modem with the speed that matches it.
7. To verify whether a modem is working properly, use modem diagnostics (Click Start, Control Panel, Phone and Modem Options, and on the Modems tab, click the modem to test. Click Properties, Diagnostics, Query Modem). Possible problems:
a. The modem diagnostics indicate that an external serial modem is not receiving commands.
Cause: If the modem diagnostics indicate that the modem is not receiving commands, the modem cabling may be faulty.
Solution: Try connecting the modem with a new cable.
b. The modem cable is good, but the modem still does not receive commands.
Cause: The modem is installed incorrectly.
Solution: Check the modem's documentation to make sure that you installed it correctly.
c. The modem is installed correctly, but the diagnostics indicate that it is not responding correctly.
Cause: The incorrect model and make were specified during installation in Windows, or an obsolete installation (.inf) file was used to install the modem.
Solution: Check the modem documentation for the correct model and make or a compatible model and make, and reinstall the modem. You can check with the manufacturer to see if there is are more recent installation files available for installing the modem.
d. According to the modem diagnostics, the modem works but you still cannot make a connection.
Cause: The modem is connected incorrectly to the phone line, or there is a problem with the phone line.
Solution: Check the connection to the phone line. If the modem is connected correctly, have a telephone professional check your phone line.
e. You cannot connect or are having problems connecting to another computer or an online service provider.
Cause: The data connection parameters (see Hardware settings) for the two modems are not the same. Data connection parameters for two modems need to be identical for them to connect successfully.
Solution: Check the hardware settings for both computers. Typical settings are eight data bits, None for parity, and one stop bit. If you are connecting to an online service provider, refer to the documentation provided by your service provider for the correct settings. These are typically eight data bits, None for parity, and one stop bit. Bulletin boards and most service providers use these settings. If these do not work, try seven data bits, even parity, and one stop bit. A few online service providers use these settings. Other settings are extremely rare.
f. Your PCMCIA modem card was not detected automatically when you inserted it.
Cause: The card's built-in COM port is not configured.
Solution: Use Add Hardware in Control Panel to configure the card's built-in COM port. You can then install the PCMCIA modem by using the Phone and Modem Options in Control Panel (See To install a modem).
g. An RS-232 serial device is functioning poorly or not at all.
Cause: Some RS-232 serial devices now support speeds faster than the 115.2 kilobits per second (Kbps) currently supported by the standard serial ports installed on most computers. (For example, some serial devices support 230 Kbps.)
Solution: If the Port speed in the connection preferences is faster than 115.2 Kbps, then try reducing the speed to 115.2 Kbps. You can leave the Maximum Port Speed in the modem properties at the higher setting. If the serial port on your computer supports speeds faster than 115.2 Kbps, then set the Port speed to whichever is slower, the serial port speed or the device speed.
h. A connection in Network Connections reports that a port is in use or not configured for remote access.
Run the "Modem Troubleshooter."
To log and view modem commands - in Logging, select Append to Log
(1) Click View Log to display the log file. This file identifies the modem and displays information about how it is functioning.
(2) Commands sent to the modem are captured in the file: Systemroot\System32\ModemLog_Model.txt.
(3) The path is usually C:\Windows\System32\. Model is the name of the modem as it appears in the list of installed modems on the Modems tab of the "Phone and Modem Options".
8. When you use or try to use an Internet browser File Transfer Protocol (FTP) or Telnet to communicate with servers on the Internet, use the information in Q314095 to help diagnose and resolve the described issues, such as:
a. The server is not functioning properly or has been temporarily removed from the Internet.
b. Your Internet browser is not configured properly.
c. The Transmission Control Protocol/Internet Protocol (TCP/IP) configuration for your dial-up connection to your ISP is incorrect.
d. Your ISP's Domain Name Service (DNS) server is not working properly.
9. Supplemental reading:
a. "Resources for Troubleshooting Modem Problems in Windows XP (Q308022)," all ALL it's related links.
b. "Troubleshooting Cable Modems (Q310089)."
c. "A General Description of IRQ Sharing in Windows XP (Q314068)."
d. "Unable to Change Resource Settings in Windows XP Device Manager (Q315278)."
e. "The Add Hardware Wizard Detects Turned-Off COM Ports in Windows XP (Q323511)."
f. "You Cannot Create a Network Connection After You Restore Windows XP (Q329442)."
g. "Cannot Load Remote Access Connection Manager" Error Message, Internet Connection Does Not Work, or Modem Does Not Work After Windows XP Upgrade (Q822122)."
h. "Understanding the differences between the two types of modems, standard and controller-less" - a TechNet article.
i. "Troubleshooting network and dial-up connections" - a TechNet article.