USB-to-serial converters add high-speed ports to tapped-out machines

When your users need extra serial ports for their numerous peripheral devices, there are several USB-to-serial port converters available. Michael Jackman gives his review of the Edgeport/2 and the Keyspan 49W adapters.

IT staff generally support desktops that require only a standard mouse, keyboard, and perhaps one extra peripheral. However, in many organizations the ability to attach multiple peripherals is vital. While desktops don't always have enough serial ports to accommodate these extra devices, products such as the Keyspan 49W and the Edgeport/2 can convert unused USB ports to useable serial ports.

Who needs more serial ports?
Other than the standard keyboard and mouse, computers need serial ports for credit card machines, smart card readers, specialty printers, cameras, bar-code scanners, drawing tablets, PDA hot-sync cradles, GPS receivers, external hard drives, wireless access points, etc.

To add to a computer’s serial ports, you can use expansion slots, but the amount of slots and available interrupts is limited. It’s also hard to expand a laptop or other mobile computer to add extra serial lines. Therefore, companies have turned to converting USB ports to serial ports. Theoretically, you could add up to 127 devices per USB port, taking care of all your serial port needs. The two models reviewed here, by Keyspan and Inside Out Networks, both have advantages and a few glitches to note.

Keys to Keyspan
Model: 49W
Type: USB 4-port serial adapter
Cost: $137.95
OSs supported: Linux 2.4 kernel or greater, Mac OS 8.6 or greater, Windows 98/Me/2000 (NT not supported)
Plusses: Attractive, runs on low-power USB ports, good installation program, speed up to 230 Kbps per port
Minuses: Modem problem, some bugs in the drivers in indicating ports in Win 98, NT support in documentation is in error (there’s no support for NT), configuration utility too complex
Web site:

Richmond, CA-based Keyspan, founded in 1995, originally developed products to connect peripherals to Macs. Its products include USB serial adapters, parallel adapters, and hubs. Recently, the company has added FireWire cards and expanded its OSs to include Microsoft Windows and Linux-powered machines.

The recently marketed 49W, shown in Figure A, is a rounded, translucent, smoke-colored device, designed in the attractive Mac-art style. A red power LED and four green status LEDs are helpful indicators of which ports are installed and functioning.

Figure A

The latest Windows drivers (1.1b11) for the peripheral were released this July. The “b” stands for beta: The company is still improving the drivers. The install process was fairly simple on my Windows 98 machine. The 49W installation program, a self-installing executable file, flawlessly sets up the drivers and the Keyspan 4-port Serial Adapter Assistant. The three-tabbed Assistant, shown in Figure B, allows users to check the status of each COM port and perform diagnostics and setup.

Figure B

You should install the drivers with the device unplugged. After the drivers are installed, plug in the device and peripherals. Windows Plug and Play will detect the new peripheral and locate the software for it. There’s no need to reboot. Once it’s running, plug in your serial devices and assign them to the new COM ports using your peripherals’ setup applets.

Keyspan isn't spic and span
In Windows 98 First Edition, the Keyspan is not reliable enough to recommend. The drivers still need refinement. However, since they are still in beta, I’m confident Keyspan will stabilize the drivers and make the product more dependable.

I tested a few serial devices. A Palm Pilot cradle worked flawlessly. However, my U.S. Robotics modem would not connect to my ISP. It would dial and begin to verify the username and password and then would be disconnected by the remote computer. Keyspan’s technical support acknowledged some reports of modem problems and asked for the model number of the modem so they could work on the issue.

Because of the way Keyspan labels the COM ports, modem setup was difficult. Figure C shows the modem configuration screen for a dial-up networking connection.

Figure C
The COM port descriptions are too long, making you have to guess which COM port the modem’s serial line is attached to.

As you can see, being at the end of a long label, the COM port number is not visible. And without that number, it’s impossible to tell which port is being viewed. This adds an unnecessary complication to installing serial ports.

The 49W’s HTML documentation is thorough but with a significant error. It states that the driver adds USB support to Windows NT. NT support is essential for any product in legacy markets. Unfortunately, when I tried to install the drivers, I received this disappointing message: Windows NT Not Supported In Beta Release.

Three other quirks are worth mentioning. First, by unplugging the device and plugging it back in again, it showed four additional COM ports, for a total of eight. In other words, the driver didn’t clear the previous ports, although they were no longer available. To help with this COM port issue, Keyspan’s Serial Adapter Assistant contains a Clean Registry utility (look under the Special item on the menu bar). To use Clean Registry, the Keyspan device must be unplugged. Once the utility is run, the ports as well as the drivers are cleared and are reinstalled when the unit is plugged in again.

The second quirk is that the port status lights are inconsistent. Lights may turn green when no serial device is attached to the ports, or they may not when a line is connected, at least not until it is transmitting.

Finally, Keyspan’s 4-Port Serial Adapter Assistant is a complex and revealing piece of software if you’re a technician interested in diagnosing communications software. For example, pressing the Data Monitor Window button in the Diagnostics tab opens a real-time log that lets users check the data flowing through the port in either ASCII or HEX mode. This is too much information for most users who want a turnkey solution: install the drivers, plug in the device, add peripherals, and go.

One advantage of the 49W is that it works in high-power or low-power mode. This means you can connect it to a computer’s standard USB port, or to a low-powered USB extension port, such as those found on newer keyboards.

I’m rooting for the Keyspan, as I think it has great potential. However, until new drivers are written to get it out of beta, it’s not ready.

Edgeport USB Converter
Edgeport edges out Keyspan
Model: Edgeport/2
Type: USB to 2-serial port adapter
Retails: $229
OSs supported: Linux 2.4.3 kernel, Mac OS 8.1 and 8.66 or greater, Windows 95/98/Me, Windows 2000, Windows NT, Windows CE
Plusses: Stable and reliable, modem function, support for Windows NT, high-speed serial ports up to 230 Kbps
Minuses: Doesn’t run on low-power USB ports, only one status light, driver can override a USB keyboard in Windows NT, higher cost
Web site:

Inside Out Networks of Austin, TX, makes a complete line of USB converters including the Edgeport, Rapidport, and Hubport external devices and an internal PCI card for adding USB ports to PCs. The Edgeport line includes two, four, and eight port units wired for different connectors. Edgeports are available for RS-232, 422, and 485 ports.

The Edgeport USB Converter, shown in Figure D, though not as artsy as the Keyspan, has the solid, rectangular look of standard networking equipment. The only concession to flair is the triangular portion in the lower left corner of the device.

Figure D

Edgeport calls these products intelligent devices. The unit I tested didn’t require any configuration; serial peripherals ran as expected the first time. I’d call that a sign of intelligence. I tested the Edgeport in Windows 98 First Edition and Windows NT 4.0 Workstation (Service Pack 6a).

Using the utility
The Edgeport USB Converter comes with a helpful utility, Edgeport.exe. The General tab on the Properties sheet lists Edgeport devices detected (see Figure E).

Figure E
Check the Edgeport devices installed and available COM ports using the Edgeport.exe utility.

You can also use the utility to:
  • Gather information about the device, including ROM date and boot code versions.
  • Configure the device by manually assigning COM port numbers.
  • Test the ports using a digital loopback test.
  • View the filenames of all driver files and their versions, sizes, dates, and descriptions.
  • Uninstall the drivers.
  • Change how COM port assignments are made (see Figure F).

Figure F
COM port assignments can be viewed and changed using the Edgeport.exe utility.

Having COM assignments based on the Edgeport’s serial number means that no matter which USB port the device is plugged into, the COM assignments travel with that unit. Basing COM port assignments on the physical USB port allows Edgeport devices to be swapped out without having to remap COM ports.

Using a modem
If you’re planning to connect a modem to the Edgeport, reassign the modem’s COM port by following these steps: In Dial Up Networking, right-click a dial-up connection and choose Properties. Next, click the Configure button for your modem. The modem’s Properties dialog will open, displaying the contents of the General tab. Under the Port drop-down menu, select an unused port. Click OK until all menus are closed. Then, dial your connection. During my tests, the modem worked perfectly.

Modem installation is just a tad more complicated in NT. Before you can use a modem with any device, it’s necessary to attach a modem to the new COM port using the Control Panel’s Modems applet. Next, add a modem to the Remote Access Service (RAS). Once you’ve installed the new modem and rebooted your computer, the modem is available on the new serial port for dial-up connections. For me, the acid test of the driver’s intelligence was whether NT could detect the modem plugged into the new COM port during modem installation. It did, querying and finally identifying the correct COM port.

Edgeport quibbles
Unlike the Keyspan, the Edgeport performed almost flawlessly. I wish, however, that the Edgeport included status lights for each port like the Keyspan does. Instead, one LED has to do the job of indicating a communications problem (red), a serial port in use (amber), and a successful connection (green).

Under Windows 98, since there is no installer program, you get no shortcut to the Edgeport utility placed on the desktop or in Start | Programs. An installer would be a nice addition to the product.

Windows 2000 will attempt to install the incorrect driver if the installation CD is used. Inside Out Networks has a special note on this issue here.

Quite by chance, I discovered another quirk. I use a Microsoft USB keyboard. The keyboard works in NT 4.0 even without USB support because my computer’s BIOS contains support for legacy devices. Essentially, the BIOS takes the keyboard IRQ from the USB and transparently redirects it to the PS/2 IRQ. When I installed the Edgeport drivers, the Microsoft keyboard stopped working because the drivers were incompatible with the legacy BIOS setting. As a workaround, Edgeport sent a USBHID driver that allowed both the Edgeport and a USB keyboard or mouse to be used.

For those times when your computer needs to have as many peripherals as an octopus has tentacles, nothing beats a USB-to-serial port converter. Of the two solutions I tested, the Edgeport proved a reliable, well-designed device with an NT USB stack included. Its utility program is helpful but not overly complicated. The Keyspan 49W would be an attractive solution because of its design, independent status lights, and ability to use a low-power USB port. However, until the drivers are up to speed, I don’t recommend it.

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