COM Ports Out of Sequence on Windows 3.x Computers - Search Again SUMMARY I want to connect my Windows 3.x computers with either my blue serial cable or with my modems using LapLink. The COM ports on my machine are set to COM1, COM2, and COM4. Is LapLink having problems connecting because my COM ports are out of sequence? SOLUTION The COM ports being out of sequence may cause the connection to fail or be unstable. In some cases, the machine may freeze. The COM ports on some machines are set this way because it originally came with two serial ports: the mouse on COM1 using IRQ 4, and the second serial port set to COM2, using IRQ 3.
When another serial device is added (an internal modem, for example) it is often set to COM4 because a COM3 port and IRQ would conflict with the mouse on COM1. (COM1 and COM3 share IRQ 4, while COM2 and COM4 share IRQ 3. Two devices cannot use the same interrupt or port at the same time.)
However Windows 3.x may be configured differently when COM ports are out-of- sequence. When the third serial device is set to COM4 as in this example, the COM4 address and IRQ shifts to the COM3 position if a COM3 port is not present when the computer is first powered on or rebooted. With this configuration, you need tell Windows 3.x to use COM3 with the address and IRQ of COM4. You can do this from the Window's Control Panel, as outlined below.
- From the Main program group, open the Windows Control Panel .
- Double-click the Ports icon.
- Click COM 3 to select this port.
- Click Settings, then the Advanced button.
- Click the down arrow next to Base I/O Port Address to display the available COM port addresses.
- Select the COM4 address, 02E8.
- Click the down arrow next to Interrupt ReQuest Line (IRQ) to display the different interrupts.
- Select 3 then click OK.
- Exit and restart Windows.
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