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LINDY CPU Switch USB Installation and Use Page 17
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 LINDY CPU Switch USB
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 LINDY CPU Switch USB is fitted with an enumeration
guard timeout system. Once the LINDY CPU Switch USB 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 LINDY CPU Switch USB may be made to autoscan the connected computers.
During autoscan the LINDY CPU Switch USB 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.