                 =============================
                 Null-modem emulator (com0com)
                 =============================

INTRODUCTION
============

The Null-modem emulator is an open source kernel-mode virtual serial
port driver for Windows, available freely under GPL license.
You can create an unlimited number of virtual COM port
pairs and use any pair to connect one application to another.
Each COM port pair provides two COM ports with default names starting
at CNCA0 and CNCB0. The output to one port is the input from other
port and vice versa.

Usually one port of the pair is used by Windows application that
requires a COM port to communicate with a device and other port is
used by device emulation program.

For example, to send/receive faxes over IP you can connect Windows Fax
application to CNCA0 port and t38modem (part of the OpenH323 project)
to CNCB0 port. In this case the t38modem is a fax modem emulation program.

The homepage for com0com project is http://com0com.sourceforge.net/.


INSTALLING
==========

NOTE (Windows Vista):
  Before installing/uninstalling the com0com driver or adding/removing/changing
  ports on Windows Vista the User Account Control (UAC) should be turned off.

NOTE (x64-based Windows Vista):
  The com0com.sys is a test-signed kernel-mode driver that will not load by
  default on x64-based Windows Vista. To enable test signing, use the following
  BCDedit command: bcdedit.exe -set TESTSIGNING ON

NOTE:
  Turning off UAC or enabling test signing will impair computer security.

Simply run the installer (setup.exe). An installation wizard will guide
you through the required steps.
If the Found New Hardware Wizard will pop up then
  - select "No, not this time" and click Next;
  - select "Install the software automatically (Recommended)" and click Next.
The one COM port pair with names CNCA0 and CNCB0 will be available on your
system after the installation.

You can add more pairs with the Setup Command Prompt:

  1. Launch the Setup Command Prompt shortcut.
  2. Enter the install command, for example:

       command> install - -

The system will create 3 new virtual devices. One of the devices has
name "com0com - bus for serial port pair emulator" and other two of
them have name "com0com - serial port emulator" and located on CNCAn
and CNCBn ports.

To get more info enter the help command, for example:

       command> help

Alternatively to setup ports you can invoke GUI-based setup utility by
launching Setup shortcut (Microsoft .NET Framework 2.0 is required).

TESTING
=======

  1. Start the HyperTerminal on CNCA0 port.
  2. Start the HyperTerminal on CNCB0 port.
  3. The output to CNCA0 port should be the input from CNCB0 port and
     vice versa.


UNINSTALLING
============

Simply launch the com0com's Uninstall shortcut in the Start Menu or remove
the "Null-modem emulator (com0com)" entry from the "Add/Remove Programs"
section in the Control Panel. An uninstallation wizard will guide
you through the required steps.

HINT: To uninstall the old version of com0com (distributed w/o installer)
install the new one and then uninstall it.


FAQs & HOWTOs
=============

Q. Is it possible to change the names CNCA0 and CNCB0 to COM2 and COM3?
A. Yes, it's possible. To change the names:

   1. Launch the Setup Command Prompt shortcut.
   2. Enter the change commands, for example:

      command> change CNCA0 PortName=COM2
      command> change CNCB0 PortName=COM3

Q. The baud rate setting does not seem to make a difference: data is always
   transferred at the same speed. How to enable the baud rate emulation?
A. To enable baud rate emulation for transferring data from CNCA0 to CNCB0:

   1. Launch the Setup Command Prompt shortcut.
   2. Enter the change command, for example:

      command> change CNCA0 EmuBR=yes

Q. The HyperTerminal test succeeds, but I get a failure when trying to open the
   port with CreateFile("CNCA0", ...). GetLastError() returns ERROR_FILE_NOT_FOUND.
A. You must prefix the port name with the special characters "\\.\". Try to open
   the port with CreateFile("\\\\.\\CNCA0", ...).

Q. My application hangs during its startup when it sends anything to one paired
   COM port. The only way to unhang it is to start HyperTerminal, which is connected
   to the other paired COM port. I didn't have this problem with physical serial
   ports.
A. Your application can hang because receive buffer overrun is disabled by
   default. You can fix the problem by enabling receive buffer overrun for the
   receiving port. Also, to prevent some flow control issues you need to enable
   baud rate emulation for the sending port. So, if your application use port CNCA0
   and other paired port is CNCB0, then:

   1. Launch the Setup Command Prompt shortcut.
   2. Enter the change commands, for example:

      command> change CNCB0 EmuOverrun=yes
      command> change CNCA0 EmuBR=yes

Q. I have to write an application connected to one side of the com0com port pair,
   and I don't want users to 'see' all the virtual ports created by com0com, but
   only the really available ones.
A. if your application use port CNCB0 and other (used by users) paired port is CNCA0,
   then CNCB0 can be 'hidden' and CNCA0 can be 'shown' on opening CNCB0 by your
   application. To enable it:

   1. Launch the Setup Command Prompt shortcut.
   2. Enter the change commands:

      command> change CNCB0 ExclusiveMode=yes
      command> change CNCA0 PlugInMode=yes

Q. When I add a port pair, why does Windows XP always pops up a Found New Hardware
   Wizard? The drivers are already there and it can install them silently in the
   background and report when the device is ready.
A. It's because there is not signed com0com.cat catalog file. It can be created on
   your test computer by this way:

   1. Create a catalog file, for example:

      cd "C:\Program Files\com0com"
      inf2cat /driver:. /os:XP_X86

   2. Create a test certificate, for example:

      makecert -r -n "CN=com0com (test)" -sv com0com.pvk com0com.cer
      pvk2pfx -pvk com0com.pvk -spc com0com.cer -pfx com0com.pfx

   3. Sign the catalog file by test certificate, for example:

      signtool sign /v /f com0com.pfx com0com.cat

   4. Install a test certificate to the Trusted Root Certification Authorities
      certificate store and the Trusted Publishers certificate store, for example:

      certmgr -add com0com.cer -s -r localMachine root
      certmgr -add com0com.cer -s -r localMachine trustedpublisher

   The inf2cat tool can be installed with the Winqual Submission Tool.
   The makecert, pvk2pfx, signtool and certmgr tools can be installed with the
   Platform Software Development Kit (SDK).

Q. How to monitor and get the paired port settings?
A. It can be done with extended IOCTL_SERIAL_LSRMST_INSERT. See example in

   http://com0com.sourceforge.net/examples/LSRMST_INSERT/tstser.cpp

Q. To transfer state to CTS and DSR they wired to RTS and DTR. How to transfer
   state to DCD and RING?
A. The OUT1 can be wired to DCD and OUT2 to RING. Use extended
   IOCTL_SERIAL_SET_MODEM_CONTROL and IOCTL_SERIAL_GET_MODEM_CONTROL to change
   state of OUT1 and OUT2.  See example in

   http://com0com.sourceforge.net/examples/MODEM_CONTROL/tstser.cpp
