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ALIF: USB

What is a USB hub?

A USB Hub allows you to connect a number of USB devices, such as mice, keyboards, USB flash drives and Printers to a single USB port on a host computer. They physically come in a variety of shapes and sizes, some are externally powered, and others derive their power from the host to which it is connected.

Infinity USB4


How Infinity uses USB

By default, an Infinity Transmitter presents itself to the host computer as 13-port USB Hub. The hub size can be reduced to 7, if required for compatiblity with much older host computers. Some older BIOS's will not work if the hub size is 13.

Port 1 of the 13-port USB Hub is taken by the Dummy keyboard (by default, optional). Older hosts will not boot passed the BIOS unless they detect a keyboard. The dummy keyboard tells the host that a keyboard is present even if the Transmitter is not connected to a Receiver.

The diagram shows two RX’s connected to the same TX. Each unique USB device takes a slot on the hub and identifies itself by using a VID and PID. A VID is a 16-bit vendor number (Vendor ID). A PID is a 16-bit product number (Product ID). 

If you exceed the 13-port limit, a banner message will tell you that it has not been able to add all of the USB devices.

Port Merging

Infinity allows you to share a single Transmitter with multiple Receivers. As each receiver connects to the same transmitter, the USB devices from each receiver consume a USB hub slot on the transmitter.


Infinity USB2



It is possible to consume all the 13-ports on the Transmitter when multiple Receivers share the same channel. Therefore, Infinity uses a system called Port Merging, which consolidates USB devices that are identical together to reduce the number of slots required. Port Merging is enabled by default. Merged devices typically remain present on the transmitter's USB hub, even if all the receivers are disconnected. This is to avoid the need to re-enumerate the USB devices again when a receiver with the same device(s) connect, to speed up the channel switching time. However, if all the USB hub slots are taken and another USB device needs to be added, the transmitter will automatically remove identical merged devices that are no longer present to free up a slot.

For example, the diagram shows identical mice and keyboards from each receiver being merged on the transmitter:-


Infinity USB5


Not only does Port Merging merge USB devices from different receivers, it also merges devices that are identical on the same receiver. This can be a problem where identical devices need to be treated differently.

For example, if you had a dual Infinity transmitter and receiver, and you connected two identical touchscreens to the receiver, by default these devices would merge. This can have unexpected results, where touching one screen actually affects the other. Therefore, it is recommended that Port Merging is disabled on the USB ports where the touchscreens are attached to the Receiver.

Infinity USB6


Enabling/Disabling Port Merging

Depending on your setup, Port merging can be enabled/disabled in the following ways:-

  • Point to Point: When connected point to point without an AIM Manager, you will need to connect directly to the Receiver's web interface. From the available menu options, choose "USB Settings". In the "Host Port Reservation" section there is a checkbox in front of four USB ports on the Receiver, i.e. Top Left, Top Right, Bottom Left and Bottom Right. To disable merging, simply untick the checkbox.

Infinity USB7


  • AIM Manager: When using an AIM Manager, there are two places where the Port Merging can be set, either globally or on an individual receiver. The most common way is to configure the receivers independently as not all receivers may have the same USB devices. On the AIM Manager, navigate to the Receivers tab and click on the edit button for the receiver with devices you do not wish to merge. On the Receivers configuration page, scroll down to the USB Settings link and click it. In the Advanced Port Features section, you untick the merging function on each of the four USB ports on the receiver. Press Save USB Settings to commit the change.

Infinity USB8

Isochronous USB Devices

An isochronous USB device must send and receive a sequence of events regularly, at equal timed intervals. Any delays in receiving the data will cause glitches and/or could cause it to stop functioning. A webcam and USB Audio are examples of devices that are isochronous.

Infinity endpoints do not support isochronous devices. However, you can use our C-USB-LAN product alongside Infinity, which is a dedicated 4-port USB hub that does support isochronous. The C-USB-LAN Transmitters and Receivers can be controlled using an AIM Manger running firmware v4.5 and above.

There are settings that can be applied to the Receivers that can display a banner message should a user connect an isochronous device, to warn them that it is not supported. By default, this setting is disabled. There is also a setting that allows you to connect a mixed USB device that contains an isochronous device. For example, if you had a keyboard with a built-in speaker or microphone. This setting will allow the keyboard element to operate, however, the isochronous component would be ignored. These settings can be found in different locations, depending on your setup. For example, in a simple point to point setup without an AIM, this is configured on the receivers web interface under the USB Configuration section. In an AIM Managed setup, these settings can be either applied Globally (Dashboard -> Settings -> Receivers -> USB Settings) or individually by going into the Receivers tab, clicking edit on an appropriate receiver and then going into the USB Settings.


Page last modified on Tuesday July 18, 2017 17:14:57 GMT-0000