DOCUMENT:Q103015  02-SEP-1993  [W_NT]
TITLE   :Configuring Advanced Options for COM Ports
PRODUCT :Windows NT
PROD/VER:3.10
OPER/SYS:WINDOWS
KEYWORDS:

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The information in this article applies to:

 - Microsoft Windows NT operating system version 3.1
 - Microsoft Windows NT Advanced Server version 3.1
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SUMMARY
=======

If you choose the Ports icon in Control Panel, you can configure the
baud rate, number of data bits, parity, number of stop bits, and flow
control for the existing standard PC communication (COM) ports, such
as COM1. If you select one of the existing standard COM ports and then
choose the Advanced button, you receive the following message:

   There are no user configurable Advanced I/O parameters for this COM
   port.

This message means that NTDETECT already has obtained all the
information about the particular port from the BIOS at boot time. To
override those detected values, advanced options such as IRQ, I/O
addresses, COM Port Number, and FIFO Enable must be set directly in
the Registry by using the REGEDT32.EXE utility (Registry Editor).

Windows NT 3.1 and Windows NT 3.1 Advanced Server support a maximum of
256 COM ports. Any ports after the existing standard COM ports can be
added and modified by choosing Ports in Control Panel.

MORE INFORMATION
================

WARNING: Registry Editor (REGEDT32.EXE) is a very powerful utility
that allows you to directly change the Registry database. Using
Registry Editor incorrectly can cause serious problems, including hard
disk corruption. It may be necessary to reinstall the software to
correct any problems. Microsoft does not support changes made with
Registry Editor. Use this tool at your own risk.

The HKEY_LOCAL_MACHINE\System\CurrentControlSet\Services\Serial subkey
in the Registry has subkeys and values that can be used change
defaults for serial ports that were detected by the system. This
subkey can also be used to override values determined by the hardware
detection.

The Serial subkey contains the subkey Parameters, under which there
can be a set of subkeys typically named Serial<X>, where <X> is a
whole number. A system administrator must place these subkeys and
values in the Registry. You can define and manipulate these values
only by editing the Registry.

Under the Serial<X> subkey, the following value entries can appear.
The first three of these value entries are required. If the subkey
does not include all three, the port is not configured, and an error
appears in the System Log in Event Viewer.

1. DosDevices      REG_SZ        Range: Free-form string

Specifies the name used to access the communication port from the
Windows NT command prompt or from within an application. A typical
value would be COM3.

2. Interrupt       REG_DWORD     Range:  A hex value

Denotes the IRQ that the particular device would interrupt on. In this
case, a typical interrupt value would be 0x4.

3. PortAddress     REG_DWORD     Range:  A hex value

Denotes the address of the first register of the serial device. In
this case, a typical PortAddress would be 0x3e8. If the PortAddress
value entry is the same as a system-detected port, the data in the
current control set is used instead of the data found by the system.
Entries appear in the System Log in Event Viewer if this is occurring.

The following entry values are optional:

4. DisablePort     REG_DWORD     Range: 0 or 1     Default: 0

If the value is 1, the device is deleted after the port is reset
during initialization. No access to the port is allowed.

5. ForceFifoEnable REG_DWORD     Range: 0 or 1     Default: 1

If the value is 1 and the hardware supports a FIFO buffer (for
example, the NS 16550AFN), the driver enables the FIFO. Not all FIFOs
are reliable. If the application or the user notices lost data or no
data transmission, it is recommended that this value be set to 0.

REFERENCES
==========

Information on the serial registry keys was obtained from the
REGENTRY.HLP file available in the Windows NT Resource Kit.

Additional reference words: 3.10 comm
KBCategory:
KBSubCategory: winnt howto

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Copyright Microsoft Corporation 1993.