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AdderView USB Installation and Use Page 15
2.4.1 Setting the USB enumeration guard time
(option switches 5 and 6)
A USB-enabled computer detects and configures USB peripherals when they are
connected to or disconnected from its USB ports. This process is called
enumeration. You can often see when the enumeration process is in progress as the
computer will usually display a timer or hourglass for a few seconds after the
connection of a USB peripheral whilst the device is being enumerated.
This enumeration process will take place each time that the AdderView locks on to a
new computer port. Unfortunately computer software is not generally robust enough
to cope with the connection between the computer and peripherals being broken
during this enumeration process. If the connection is lost part of the way through the
enumeration process then the computer software or the peripherals can hang.
To overcome this problem the AdderView is fitted with an enumeration guard timeout
system. Once the AdderLink has locked on to a channel it will remain connected to
that channel for at least the enumeration guard time. This ensures that the
enumeration process is complete before further channel changes are allowed and
consequently ensures robust and reliable operation.
The enumeration process takes longer if more peripherals are connected. Select an
enumeration time that is longer than the longest observed enumeration time. The
enumeration time can be judged by the length of time that the hourglass or timer
remains on the computer screen after a channel change (normally a few seconds).
Alternatively you may select the shortest enumeration guard time (2 seconds) and
remember not to change the channel whilst the hourglass or timer is displayed.
2.4.2 Setting the autoscan dwell time
The AdderView may be made to autoscan the connected computers. During
autoscan the AdderView displays the video signal from each computer in turn for a
selected time period. This time period is known as the dwell time and may be
selected to be 2 or 5 seconds using option switch 7. Ports are scanned in ascending
numerical sequence and all the ports or just the active ports will be scanned
according to the setting of option switch 8.