Adder Technology AV4USB-MAC, AV4USB-PC Setting the USB enumeration guard time option switches 5

2.4.1Setting 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.

AdderView USB Installation and Use Page 15