Product specifications

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True USB Emulation
However, although emulated switches cured a number of shortfalls
associated with their enumerated cousins, there was still one main
limitation to their operation. It remained a complex task to dynamically
assume the identity of a USB device, distribute it among the connected
computers, and maintain all the necessary signals, states, and processes.
True USB Emulation
True USB emulation was developed to overcome the limitations associated
with even emulated USB switching techniques.
With true USB emulation, the complete identity of the keyboard and
mouse can be copied and then presented, fully supported, to all the
connected computers. This means that any keyboard offering special
function keys or any mouse with extra features will be fully supported at
each computer — instantly, with no latency. As with the previous emulation
method, the unselected computers continue to see the identities of the
keyboard and mouse, which means that no enumeration is necessary
when their link becomes active once again. This not only helps to make
reconnecting faster, it also increases switching reliability. This is important
because USB links are at their most vulnerable during the enumeration
process.
A high-speed circuit fully emulates the USB device identities, and it
interprets keyboard and mouse data streams. The result is full support
for KVM switching via hotkey presses or the third button/scroll wheel
of a mouse. For local installations, this is useful; for remote applications,
such as KVM over IP, it’s essential.
Because other USB devices don’t necessarily need the benefits of true
emulation like USB keyboards and mice do, there are one or even two
enumerated circuits along the true USB emulation feature. This enables
the other USB devices to operate at their highest speeds without any
intervention. The enumerated circuits benefit greatly from the USB hubs
that are jointly used with the true emulation system. Because they interface
directly and permanently with each computer, they help to stabilize
the dormant links, making errors during enumeration much less likely.
The dual switching arrangement provides further flexibility because
the true emulation and enumerated sections can be switched in unison
or independently of each other, as required. Thus, various peripherals
can operate with different computers at the same time.
The inside view of a true emulation USB switch.
The emulated section of the switch is shown in blue and handles only
the keyboard and mouse. This section relies heavily on the emulation
engine, a custom circuit that is closely allied with each of the USB hubs.
These ensure that all connections to the computers remain active.
The enumerated section of the switch is shown in green and handles
other USB devices and also uses the USB hubs to link with the
computers.
PC 1
Host Controller
Emulation
Engine
PC 2 PC 3 PC 4
USB
Hub
USB
Hub
USB
Hub
USB
Keyboard
USB Mouse USB Device
USB
Hub