Installation of COM ports in Windows NT

This document details the installation of COM: ports under Windows NT. Installation notes are included for Non-Intelligent Multi-port and Normal serial interfaces. Non-Intelligent Multi-port serial interfaces are special COM: cards that have an Interrupt Status Register that allows the Device Driver to better service the ports that reside on the card.

WARNING: Be very careful when following the procedure for adding ports. If an error is made, you may need to use the emergency repair disk to recover.

To configure multi-port serial adapters for Windows NT.

  1. Determine the best IRQ and port address values for your adapter to use in your computer.

  2. Install the adapter according to the manufacturer's instructions.

  3. Using Registry Editor, open the key HKEY_LOCAL_MACHINE\SYSTEM\Currentcontrolset\Services\Serial\Parameters (For more information on how to do this, see the on-line help for Registry Editor.)

  4. From the appropriate table below, add the Serial* Keys under Parameters and add the corresponding values for each Serial* key. The actual values for your computer may be different. Also, if you have only one serial port on your computer, you may start with Serial1 and Com2:. If no serial ports are built into your computer, you may start with Serial0 and Com1:.

  5. If there are no serial ports built into your computer, the following values need to be added under the HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\Serial:
Add Value Names         Data Type       Data
ErrorControl REG_DWORD 1 Group REG_SZ Extended base Start REG_DWORD 2 Type REG_DWORD 1

Exit from Regedt32, and enter the following 2 commands to activate the changes:

Sample Configuration Key Values
The sample below assumes that there are two serial ports already available that will be listed as "Serial0" and "Serial1" in the Registry and assigned to COM1: and COM2: respectively. The additional ports will start at COM3:. For more than four port adapters, simply continue the pattern for as many ports as needed.

Example : Quadport 4-port adapter at IRQ10, starting port address 500, starting at COM3:.

You must program the Interrupt Pending Register for the Quadport at 0x0140 or another free range.

The IRQ Pending register will occupy 8 contiguous locations (ie. 0x0140..0x0147)

Serial0 = COM1 and Serial1 = COM2

Add Key              Add Value Names      Data Type       Data
(no class)

Serial2 PortAddress REG_DWORD 0x500 Interrupt REG_DWORD 0x0a DosDevices REG_SZ COM3 PortIndex REG_DWORD 1 InterruptStatus REG_DWORD 0x140 Serial3 PortAddress REG_DWORD 0x508 Interupt REG_DWORD 0x0a DosDevices REG_SZ COM4 PortIndex REG_DWORD 2 InterruptStatus REG_DWORD 0x140 Serial4 PortAddress REG_DWORD 0x510 Interrupt REG_DWORD 0x0a DosDevices REG_SZ COM5 PortIndex REG_DWORD 3 InterruptStatus REG_DWORD 0x140 Serial5 PortAddress REG_DWORD 0x518 Interupt REG_DWORD 0x0a DosDevices REG_SZ COM6 PortIndex REG_DWORD 4 InterruptStatus REG_DWORD 0x140 NOTE : You must activate the Quadport IRQ Pending register and apply that value in the above structure for the IRQ sharing feature to function.

This feature is available on any of the Quadport products using the latest control software.

Also ensure that the IRQ you are selecting is truly conflict free and not used by another ISA / PCI bus product.

Currently Windows NT supports up to 256 COM: ports although the command line MODE does not support over COM9:.