The original application, written in VB 6, uses MSComm to open, write, read, and close a connection to PORT 1. New LAPTOP computers do not have a serial port. As a result, a Serial to USB cable is used. Because this cable can be connected and disconnected, how can I associate the old serial port 1 to the USB connection in the VB6 application?.
-->Definition
Exceptions
Access is denied to the port.
![Serial Port Vs Mscomm Serial Port Vs Mscomm](/uploads/1/2/6/3/126338756/164787239.gif)
![Serial Serial](http://assets.devx.com/articlefigs/15418.jpg)
-or-
The current process, or another process on the system, already has the specified COM port open either by a SerialPort instance or in unmanaged code.
One or more of the properties for this instance are invalid. For example, the Parity, DataBits, or Handshake properties are not valid values; the BaudRate is less than or equal to zero; the ReadTimeout or WriteTimeout property is less than zero and is not InfiniteTimeout.
The port name does not begin with 'COM'.
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The file type of the port is not supported.
The port is in an invalid state.
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An attempt to set the state of the underlying port failed. For example, the parameters passed from this SerialPort object were invalid.
The specified port on the current instance of the SerialPort is already open.
Examples
The following code example demonstrates the use of the SerialPort class to allow two users to chat from two separate computers connected by a null modem cable. In this example, the users are prompted for the port settings and a username before chatting. This code example is part of a larger code example provided for the SerialPort class.
Remarks
Only one open connection can exist per SerialPort object.
The best practice for any application is to wait for some amount of time after calling the Close method before attempting to call the Open method, as the port may not be closed instantly.
Security
SecurityPermission
for calling unmanaged code. Associated enumeration: UnmanagedCode Security action: LinkDemand
for calling unmanaged code. Associated enumeration: UnmanagedCode Security action: LinkDemand