Microsoft Windows refers to serial ports as line printer ports; if the workstation includes two serial ports, the operating system labels the first connector as LPT1 and the second connector as LPT2. Like all hardware, serial ports require device drivers to communicate with the OS; if LPT1 or LPT2 stop working, the associated driver could be at fault. Hardware conflicts can also prevent Windows 7 from communicating with the serial port. LPT uses an interrupt request to tell the processor to perform a specific action; if the port is sharing an IRQ assignment with another hardware component, the component could prevent the port from "talking" to the processor.
Click "Start," enter "device" into the search field and then select "Device Manager" from the results under Control Panel.
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Double-click "Ports (COM & LPT)" and then right-click the device marked "LPT1" or "LPT2."
Select "Properties" from the context menu to view the device properties. Check the Device Status field for an error message and code.
Look up the error code, if applicable, on Microsoft Support (see the link in the Resources) to learn how to resolve the issue. Otherwise, select the "Driver" tab.
Click "Uninstall" and follow the on-screen prompts to remove the driver. Restart the computer .
Open Device Manager, click "Action" on the menu bar and then click "Add Legacy Hardware."
Follow the on-screen instructions in the Add Hardware Wizard to reinstall the serial port.
Test the serial port. Return to Device Manager if the device still fails to work and select "View" from the menu bar.
Click "Resources by Type." Double-click "Interrupt Request (IRQ)" and then browse through the list of devices to locate the serial port.
Double-click the IRQ and then select the "Resources" tab. Check the information under Conflicting Device List to see if another device is using the same IRQ as the serial port.
Check "Use Automatic Settings" if the option is unchecked to see if the error resolves. Otherwise, select a different configuration from the "Setting Based On" drop-down menu.
Check the Conflicting Device List to see the status of the IRQ. Repeat the preceding step, if applicable, until the message "No Conflicts" appears in the box.
Click "OK" to close each window and save your changes.