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However it works fine when you start the PC in Command Prompt
mode (DOS mode).
When you are running Windows 98 Second Edition or Windows
Millennium Edition (ME) on a computer that supports the Advanced
Configuration and Power Interface (ACPI) specification, MS-DOS-based
programs that use the Extended Communication Service Int
14h function 05 do not work during the first attempt. To
observe this behavior, use the Mode.com tool, type MODE COMx:19200
, and then press ENTER. You then receive the following error
message:
Function not supported
on this computer.
NOTE : The information in this article is applicable only
if you are able to start your computer to an MS-DOS prompt
and you are able to run the preceding command successfully.
If you receive an error message when you run the preceding
command, your computer's Basic Input/Output System (BIOS)
does not support the extended communication INT 14h function
05 command. For additional information about this issue,
click the article number below to view the article in the
Microsoft Knowledge Base:
Q119595
- Function Not Supported on This Computer
This behavior can occur because the virtual communication
device (Vcd.vxd) incorrectly initializes the default state
of the COM ports for MS-DOS virtual machines (VMs) when you
start your computer because the COM ports have already been
detected and powered off. The virtual COM ports are initialized
with 0xFF for all of its states instead of the actual values
of the port. Each time a new VM is created, the default state
that was detected at startup is copied to the VM. Because
the COM ports are trapped and virtualized, some of the responses
to in/out commands are based on the default state at startup
instead of the current state of the hardware. There are many
in/out commands that non-virtualize the port. When this occurs,
power is applied to the port, the current state is copied
into the virtual settings, and the COM ports operate properly.
To work around this behavior, disable the power management
of the COM ports:
- Use Registry Editor (Regedit.exe) to locate the EnablePowerManagement value
in the following registry key:
HKEY_LOCAL_MACHINE\System\CurrentControlSet\Services\VxD\VCOMM
- On the Edit menu, click Modify , change 01 to 00,
and then click OK .
- Quit Registry Editor.
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