How are the COM Ports for My USB Serial Device Assigned?Hardware: Serial>>RS-232>>USB-232, Serial>>RS-232>>USB-232/2, Serial>>RS-232>>USB-232/4, Serial>>RS-485>>USB-485, Instrument Connectivity Other>>USB>>USB-485/2, Instrument Connectivity Other>>USB>>USB-485/4
Problem: I'm using an USB serial device like the USB-232. When I plug in my device, I always get the same COM ports assigned to it. If I plug in a second USB-232, it is assigned different ports, even if the first USB-232 is not still plugged in. Why does that happen? How are the ports assigned? Solution: The NI-Serial driver has functionality that allows it to keep track of serial port properties, including COM port numbers. For example, say there are two USB-232 and each port of each device is connected to a different instrument. Each instrument has different serial properties. So each serial port will have to have these same properties. The Windows registry is used to store this information by serial number (of the USB device) and port number. This way, each time you plug in the USB-232into that computer, it will automatically have the same properties. That way, you do not have to configure the port everytime you plug in the device. This means that when a new box is plugged in, it has to have default information as well as new COM ports numbers that are not already taken by other devices. This functionality is very useful to most users. If this is not how you want your hardware to behave, there is a simple way to reassign COM ports that are unused. After you have unplugged the original USB-232 from your computer, you'll need to open Measurement & Automation Explorer (MAX). In MAX select Tools»NI-Serial»Recover Unused Com Numbers. This clears the Windows registry of all ports that are not currently connected. Related Links: USB Serial Interfaces Product Page Attachments:
Report Date: 11/07/2008 Last Updated: 11/11/2008 Document ID: 4R69QEYW |
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