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General Technical Reference
Question 1
Why does the port stop responding when I use a program to fast open/close the port? On the other
hand, if I just do a normal port open/close, the port will stop responding after about 100 times. In a
related problem, if I use the port on a dial-up network, the port will sometimes stop responding, or
when I add a new modem under Windows XP, the port will be dead the first time I use the modem.
Answer 1
For all of these problems, simply unplug and then re-plug NPort 1220/1240 from the computer’s USb
port.
Question 2
NPort 1220/1240 currently supports baud rates from 600 bps to 115200 bps. However, if I set an
invalid baud rate, such as 300 bps, the driver does not return an error.
Answer 2
This problem stems from the fact that some Windows operating systems do not alert the user to the
baud rate limits of connected devices.
Question 3
Why is it that when I use NPort 1220/1240 under Windows XP, the OS loading is sometimes around
45%?
Answer 3
This problem is a common characteristic that appears when using USB devices under Windows XP.
Question 4
When I install NPort 1220/1240 under Windows 2000/XP, the COM port number is assigned by
which USB slot I use to connect to my computer. What happens if I change the USB slot?
Answer 4
The port number will change. Keep in mind that the port number is automatically assigned by the OS.
Question 5
Under Windows 2000, it seems that the more USB ports I install (e.g., close to 25 or 30 ports), the
port throughput drops to around 1%. How do I get around this problem?
Answer 5
We recommend limiting to 16 ports the number of USB ports installed under Windows 2000.
NPort 1220/1240 USB-to-Serial Hub User’s Manual
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