High Sec Labs SK21D-3 User manual

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Section 1 - Introduction
2-PORT SINGLE-HEAD SECURE KVM: SK21D-3 –DVI-I VIDEO, SK21P-3 –DISPLAYPORT VIDEO, SK21H-3 –HDMI VIDEO
Products covered by this manual:
2-Port Single-Head Secure KVMs:

SK21D-3 –DVI-I Video

SK21P-3 –DisplayPort Video

SK21H-3 –HDMI Video
Rev: E
Doc No.: HDC10346
2-Port Single-Head Secure KVM Switch User Manual

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2-PORT SINGLE-HEAD SECURE KVM: SK21D-3 –DVI-I VIDEO, SK21P-3 –DISPLAYPORT VIDEO, SK21H-3 –HDMI VIDEO
Table of Contents
Introduction ....................................................................................... 3
Intended Audience............................................................................. 3
Package Contents .......................................................................... 3
Revision.......................................................................................... 3
Safety Precautions ......................................................................... 4
Safety Precautions (French)........................................................... 5
User Guidance & Precautions........................................................ 6
Main Features................................................................................ 8
Tamper Evident Labels ................................................................ 10
Active Anti-Tampering System .................................................... 10
Product Enclosure Warning Label ............................................... 10
Equipment Requirements............................................................ 11
Front Panel Features –SK21D-3 (DVI-I); SK21P-3 (DP); SK21H-3
(HDMI) ......................................................................................... 13
Rear Panel Features –SK21D-3 ................................................... 14
Product Specifications ................................................................. 15
Before Installation ....................................................................... 16
Installation ....................................................................................... 17
Typical system installation........................................................... 18
Operation......................................................................................... 19
Operating the Product................................................................. 19
Troubleshooting Guide .................................................................... 21
COPYRIGHT AND LEGAL NOTICE.................................................. 24

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Section 1 - Introduction
2-PORT SINGLE-HEAD SECURE KVM: SK21D-3 –DVI-I VIDEO, SK21P-3 –DISPLAYPORT VIDEO, SK21H-3 –HDMI VIDEO
Introduction
Thank you for purchasing this High Sec Labs (HSL) Secure product
designed for use in secure defense and intelligence installations.
The product provides the highest security safeguards and features
that meet today’s IA (information assurance) computing
requirements as defined in the latest PSS Protection Profile Rev 3.0.
This User Manual provides all the details you’ll need to install and
operate your new product.
Intended Audience
This document is intended for the following professionals:
•System Administrators/IT Managers
•End Users
Package Contents
Inside product packaging you will find the following:
HSL Secure KVM Product
DC Power Supply
User Guidance Documentation
Revision
A –Initial Release, 24 Feb 2015
B –Corrections, 28 March 2015
C –Rev change, 12 May 2015
D –User Guidance updates, 21 June 2015
E –Correction to Features section, 13 August 2015
Important Security Note:
If you are aware of potential security vulnerability while
installing or operating this product, we encourage you to
contact us immediately in one of the following ways:
Web form: http://www.highseclabs.com/support/case/
Email: [e-mail]
Tel: [phone] or [phone]
Important: This product is equipped with always-on active anti-
tampering system. Any attempt to open the product enclosure
will activate the anti-tamper triggers and render the unit
inoperable and warranty void.

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2-PORT SINGLE-HEAD SECURE KVM: SK21D-3 –DVI-I VIDEO, SK21P-3 –DISPLAYPORT VIDEO, SK21H-3 –HDMI VIDEO
Section 4 - Operation
Safety Precautions
Please read the following safety precautions carefully before using
the product:
• Before cleaning, disconnect the product from any electrical power
supply.
• Do not expose the product to excessive humidity or moisture.
• Do not store or use for extensive period of time in extreme thermal
conditions –it may shorten product lifetime.
• Install the product only on a clean secure surface.
• If the product is not used for a long period of time, disconnect it
from electrical power.
• If any of the following situations occurs, have the product checked
by an HSL qualified service technician:
oLiquid penetrates the product’s case.
oThe product is exposed to excessive moisture, water
or any other liquid.
oThe product is not working well even after carefully
following the instructions in this user’s manual.
oThe product has been dropped or is physically
damaged.
oThe product shows obvious signs of breakage or
loose internal parts.
oIn case of external power supply –If power supply
overheats, is broken or damaged, or has a damaged
cable.
• The product should be stored and used only in temperature and
humidity controlled environments as defined in the product’s
environmental specifications.
• Never attempt to open the product enclosure. Any attempt to open
the enclosure will permanently damage the product.
• The product contains a non-replaceable internal battery. Never
attempt to replace the battery or open the enclosure.
• This product is equipped with always-on active anti-tampering
system. Any attempt to open the product enclosure will activate the
anti-tamper triggers and render the unit inoperable and warranty
void.

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2-PORT SINGLE-HEAD SECURE KVM: SK21D-3 –DVI-I VIDEO, SK21P-3 –DISPLAYPORT VIDEO, SK21H-3 –HDMI VIDEO
Section 4 - Operation
Safety Precautions (French)
Veuillez lire attentivement les précautions de sécurité suivantes
avant d’utiliser le produit:
Avant nettoyage, débranchez l’appareil de
l’alimentation DC / AC.
Assurez-vous de ne pas exposer l’appareil à une
humidité excessive.
Assurez-vous d’installer l’appareil sur une surface
sécurisée propre.
Ne placez pas le cordon d’alimentation DC en
travers d’un passage.
Si l’appareil n’est pas utilisé de longtemps, retirez
l’alimentation murale de la prise électrique.
L’appareil devra être rangé uniquement dans des
environnements à humidité et température
contrôlées comme défini dans les caractéristiques
environnementales du produit.
L’alimentation murale utilisée avec cet appareil
devra être du modèle fourni par le fabricant ou un
équivalent certifié fourni par le fabricant ou
fournisseur de service autorisé.
Si une des situations suivantes survenait, faites
vérifier l’appareil par un technicien de
maintenance qualifié:
oEn cas d'alimentation externe - L’alimentation
de l’appareil surchauffe, est endommagée,
cassée ou dégage de la fumée
oou provoque des court circuits de la prise du
secteur.
oUn liquide a pénétré dans le boîtier de
l’appareil.
oL’appareil est exposé à de l’humidité excessive
ou à l’eau.
oL’appareil ne fonctionne pas correctement
même après avoir suivi attentivement les
instructions contenues dans ce guide de
l’utilisateur.
oL’appareil est tombé ou est physiquement
endommagé.
oL’appareil présente des signes évidents de
pièce interne cassée ou desserrée
oL’appareil contient une batterie interne. La
batterie n’est pas remplaçable. N’essayez
jamais de remplacer la batterie car toute
tentative d’ouvrir le boîtier de l’appareil
entraînerait des dommages permanents à
l’appareil.
oCe produit est équipé d'toujours-sur le système
anti-sabotage active. Toute tentative d'ouvrir
le boîtier du produit va activer le déclencheur
anti-sabotage et de rendre l'unité vide
inutilisable et garantie.

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2-PORT SINGLE-HEAD SECURE KVM: SK21D-3 –DVI-I VIDEO, SK21P-3 –DISPLAYPORT VIDEO, SK21H-3 –HDMI VIDEO
Section 4 - Operation
User Guidance & Precautions
Please read the following User Guidance & Precautions carefully
before using the product:
1. As product powers-up it performs a self-test procedure. In
case of self- test failure for any reason, including jammed
buttons, the product will be Inoperable. Self-test failure will
be indicated by the following abnormal LED behavior:
a. All channel-select LEDs will be turned ON and
then OFF;
b. A specific, predefined LED combination will be
turned ON;
c. The predefined LED combination will indicate the
problem type (jammed buttons, firmware integrity).
Try to power cycle product. If problem persists please
contact your system administrator or technical support.
2. Product power-up and RFD behavior:
a. By default, after product power-up, the active
channel will be computer #1, indicated by the
applicable front panel push button LED lit.
b. Product Restore-to-Factory-Default (RFD) function is
available via a physical control button on rear panel.
Use a sharp object or paper clip to hold RFD button
pressed for several seconds to initiate an RFD action.
c. RFD action will be indicated by front panel LEDs
blinking all together.
d. When product boots after RFD, keyboard and mouse
will be mapped to the active channel #1 and default
settings will be restored, erasing all user-set
definitions.
3. The appropriate usage of peripherals (e.g. keyboard, mouse,
display, authentication device) is described in detail in this
User Manual's appropriate sections. Do not connect any
authentication device with an external power source to
product.
4. For security reasons products do not support wireless
keyboards and mice. In any case do not connect wireless
keyboard/mouse to product.
5. For security reasons products do not support
microphone/line-in audio input. In any case do not connect a
microphone to product audio output port, including
headsets.
6. Product is equipped with always-on active anti-tampering
system. Any attempt to open product enclosure will activate
the anti-tamper system indicated by all channel-select LEDs
flashing continuously. In this case, product will be inoperable
and warranty void. If product enclosure appears disrupted or
if all channel-select LEDs flash continuously, please remove
product from service immediately and contact technical
support.
7. In case a connected device is rejected in the console port
group the user will have the following visual indications:
a. When connecting a non-qualified keyboard, the
keyboard will be non-functional with no visible
keyboard strokes on screen when using the
keyboard.
b. When connecting a non-qualified mouse, the mouse
will be non-functional with mouse cursor frozen on
screen.

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2-PORT SINGLE-HEAD SECURE KVM: SK21D-3 –DVI-I VIDEO, SK21P-3 –DISPLAYPORT VIDEO, SK21H-3 –HDMI VIDEO
Section 4 - Operation
c. When connecting a non-qualified display, the video
diagnostic LED will flash green and video will not
work.
d. When connecting a non-qualified USB device, fUSB
LED will flash green and USB device will be
inoperable.
8. Do not connect product to computing devices:
a. That are TEMPEST computers;
b. That include telecommunication equipment;
c. That include frame grabber video cards;
d. That include special audio processing cards.
9. Product has a remote control port in the back panel labeled
RCU. Do not use this port - it is inoperable and for future use.
10. Important! Before re-allocating computers to channels, it is
mandatory to power cycle product, keeping it powered OFF
for more than 1 minute.
11. Product log access and administrator configuration options
are described in product Administrator Guide.
12. Authentication session will be terminated once product
power is down or user intentionally terminates session.
13. If you are aware of any potential security vulnerability while
installing or operating product, please remove product from
service immediately and contact us in one of the ways listed
in this manual.

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2-PORT SINGLE-HEAD SECURE KVM: SK21D-3 –DVI-I VIDEO, SK21P-3 –DISPLAYPORT VIDEO, SK21H-3 –HDMI VIDEO
Section 4 - Operation
Main Features
Product is designed, manufactured and delivered in security-
controlled environments. Below is a summaty of the main advanced
features incorporated in product:
NIAP PPS Ver. 3.0 compliant
HSL product is designed from scratch to comply with latest NIAP PPS
ver. 3.0 standard. Thoroughly tested, product meets international
NIAP security requirements and covers latest technologies:
Optimized for USB (USB 1.1, 2.0, 3.0 and Type C) to support
newest peripherals;
Optimized for HDMI and DisplayPort video;
Enables newer protocols such as MHL to support mobile
devices and not only computers;
Supports modern user interaction modes, such as cursor
control, touch-screen, multi-touch, and more.
Advanced isolation between computers and shared peripherals
The emulations of keyboard, mouse and display EDID, prevent direct
contact between computers and shared peripherals. Product design
achieves maximal security by keeping the video path separate with
keyboard and mouse switched together, purging keyboard buffer
when switching channels. All these features contribute to strong
isolation between computer interfaces, maintained even when
product is powered off.
Unidirectional data flow: USB, audio and video
Unique hardware architecture components prevent unauthorized
data flow, including:
Optical unidirectional data flow diodes in the USB data path
that filtrate and reject unqualified USB devices;
Secure analog audio diodes that prevent audio
eavesdropping at TEMPEST level with no support for
microphone or any other audio-input device;
Video path is kept separate from all other traffic, enforcing
unidirectional native video flow. EDID emulation is done at
power up and blocks all EDID/MCCS writes. For DisplayPort
video, filtration of AUX channel exists to reject unauthorized
transactions.
Isolation of power domains
Complete isolation of power domains prevents signaling attacks.
Secure administrator access & log functions
Product incorporates secure administrator access and log functions
to provide auditable trail for all product security events, including
battery backup life for anti-tampering and log functions. Non-
reprogrammable firmware prevents the ability to tamper with
product logic.
Always-on, active anti-tamper system
Active anti-tampering system prevents malicious insertion of
hardware implant such as wireless key-logger inside product
enclosure. Any anti-tampering attempt causes isolation of all
computers and peripheral devices rendering product inoperable and
showing clear indications of tampering event to user.
Holographic security tamper-evident labels are placed on the
enclosure to provide a clear visual indication if product has been
opened or compromised.
Metal enclosure is designed to resist mechanical tampering with all
microcontrollers protected against firmware-read, modification and
rewrite.

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2-PORT SINGLE-HEAD SECURE KVM: SK21D-3 –DVI-I VIDEO, SK21P-3 –DISPLAYPORT VIDEO, SK21H-3 –HDMI VIDEO
Section 4 - Operation
Main Features (Cont.)
"Freeze Audio" feature
Dedicated "Freeze Audio" push button on front panel enables to lock
this function to a specific channel in a way that switching between
channels leaves the audio function locked to current channel.
Small form factor:
Small form factor product occupying minimum desktop space.
Video Support
SK21D-3 supports DVI-I displays as well as VGA and HDMI
via compatible cables.
SK21P-3 supports DisplayPort1.1 & 1.2 displays.
SK21H-3 supports HDMI displays.
Resolutions Supported
Products support video resolutions of up to 4K-2K Ultra HD (3840 X
2160 pixels).

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2-PORT SINGLE-HEAD SECURE KVM: SK21D-3 –DVI-I VIDEO, SK21P-3 –DISPLAYPORT VIDEO, SK21H-3 –HDMI VIDEO
Section 4 - Operation
Tamper Evident Labels
Product uses holographic tamper evident labels to provide visual
indications in case of an enclosure intrusion attempt. When opening
product packaging inspect the tampering evident labels.
If for any reason one or more tamper-evident label is missing,
appears disrupted, or looks different than the example shown here,
please call Technical Support and avoid using that product.
Active Anti-Tampering System
Product is equipped with always-on active anti-tampering system. If
mechanical intrusion is detected by this system, the Product will be
permanently disabled and all LEDs will blink continuously.
If product indicates "tampered state" (all LEDs blinking) - please call
Technical Support and avoid using that product.
Product Enclosure Warning Label
Product has the following warning sticker placed in a prominent
location on product enclosure:
HSL Tamper Evident Label

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2-PORT SINGLE-HEAD SECURE KVM: SK21D-3 –DVI-I VIDEO, SK21P-3 –DISPLAYPORT VIDEO, SK21H-3 –HDMI VIDEO
Section 4 - Operation
Equipment Requirements
Cables
It is highly recommended to use HSL Cable Kits for product to ensure
optimal security and performance.
One Cable Kit is required per connected computer.
Operating Systems
Product is compatible with devices running on the following
operating systems:
• Microsoft® Windows®
• Red Hat®, Ubuntu® and other Linux® platforms
• Mac OS® X v10.3 and higher.
USB Keyboard console port
The product console USB keyboard port is compatible with Standard
USB keyboards.
Notes:
a. Console USB keyboard and mouse ports are switchable, i.e.
you can connect keyboard to mouse port and vice versa.
However, for optimal operation it is recommended to
connect USB keyboard to console USB keyboard port and
USB mouse to console USB mouse port.
b. For security reasons products do not support wireless
keyboards. In any case do not connect wireless keyboard to
product.
c. Non-standard keyboards, such as keyboards with integrated
USB hubs and other USB-integrated devices, may not be fully
supported due to security policy. If they are supported, only
classical keyboard (HID) operation will be functional. It is
recommended to use standard USB keyboards.
USB Mouse console port
The product console USB mouse port is compatible with standard
USB mice.
Notes:
a. Console USB keyboard and mouse ports are switchable, i.e.
you can connect keyboard to mouse port and vice versa.
However, for optimal operation it is recommended to
connect USB keyboard to console USB keyboard port and
USB mouse to console USB mouse port.
b. Console USB mouse port supports Standard KVM Extender
composite device having a keyboard/mouse functions.
c. For security reasons products do not support wireless mice.
In any case do not connect wireless mouse to product.
User Audio Devices
Product is compatible with the following types of user audio
devices:
Stereo headphones;
Amplified stereo speakers.
Note: In any case do not connect a microphone to product audio
output port including headsets.

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2-PORT SINGLE-HEAD SECURE KVM: SK21D-3 –DVI-I VIDEO, SK21P-3 –DISPLAYPORT VIDEO, SK21H-3 –HDMI VIDEO
Section 4 - Operation
User Display
Product console video port is compatible with the following types of
displays:
SK21D-3 supports DVI-I displays as well as VGA and HDMI
via compatible cables.
SK21P-3 supports DisplayPort1.1/1.2 displays.
SK21H-3 supports HDMI displays.

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2-PORT SINGLE-HEAD SECURE KVM: SK21D-3 –DVI-I VIDEO, SK21P-3 –DISPLAYPORT VIDEO, SK21H-3 –HDMI VIDEO
Section 4 - Operation
Front Panel Features –SK21D-3 (DVI-I);
SK21P-3 (DP); SK21H-3 (HDMI)

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2-PORT SINGLE-HEAD SECURE KVM: SK21D-3 –DVI-I VIDEO, SK21P-3 –DISPLAYPORT VIDEO, SK21H-3 –HDMI VIDEO
Section 4 - Operation
Rear Panel Features –SK21D-3
Computer interface group:
DC power supply
port
Restore to
factory default
USB Type-B for
Keyboard / Mouse
Console ports group:
Audio input jack
(3.5mm stereo)
DVI-I video port
& LED
DVI-I video port
Remote Control –
non operative,
for future use
USB
keyboard/
mouse ports
Audio input jack
(3.5mm stereo)
Note: the model described in above image is SK21D-3 (DVI-I video).
The other models are identical except for the following:
a. SK21P-3 (console: HDMI port, computer interface area: DisplayPort port).
b. SK21H-3 (HDMI video port).

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2-PORT SINGLE-HEAD SECURE KVM: SK21D-3 –DVI-I VIDEO, SK21P-3 –DISPLAYPORT VIDEO, SK21H-3 –HDMI VIDEO
Section 4 - Operation
Product Specifications
Enclosure: Steel metal enclosure
Power Requirements: DC input 12V / 1.5A maximum
No. of Users Supported: 1
No. of Computers Supported: 2
No. of Displays Supported: 1
Console Keyboard Input: USB Type-A female connector
Console Mouse Input: USB Type-A female connector
Resolution Support up to 4K-2K Ultra HD (3840 X 2160
pixels) resolutions
Console Display Port 1 x DVI-I female connector
(SK21D-3 model)
1 x HDMI female connector
(SK21P-3 & SK21H-3 models)
Console Audio input jack: 3.5mm stereo female jack
Computer Keyboard/Mouse ports: USB Type B
Computer Audio Input plug: 1/8" (3.5mm) stereo plug
Front Panel indicators CAPS LOCK, NUM LOCK, SCL LOCK
Freeze Audio
Computer Video Input plug:
1 x DVI-I video port (SK21D-3 model)
1 x DisplayPort video port (SK21P-3 model)
1 x HDMI video port (SK21H-3 model)
Port Selector illuminated push-buttons & LEDS: 2
User Channel Selection Methods: Front panel push-buttons
Operating Temp: 32° to 104° F (0° to 40° C)
Storage Temp: -4° to 140° F (-20° to 60° C)
Humidity: 0-80% RH, non-condensing
Product design life-cycle: 10 years
Warranty: 2 years

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2-PORT SINGLE-HEAD SECURE KVM: SK21D-3 –DVI-I VIDEO, SK21P-3 –DISPLAYPORT VIDEO, SK21H-3 –HDMI VIDEO
Section 4 - Operation
Before Installation
Unpacking the Product
Before opening the product packaging, inspect the packaging
condition to assure that product was not damaged during delivery.
When opening the package, inspect that the product Tamper Evident
Labels are intact.
Where to locate the Product?
The enclosure of the product is designed for desktop or under the
table configurations. An optional Mount Kit is available.
Product must be located in a secure and well protected environment
to prevent potential attacker access.
Consider the following when deciding where to place product:
Product front panel must be visible to the user at all times.
The location of the computers in relation to the product and
the length of available cables (typically 1.8 m)
Warning: Avoid placing cables near fluorescent lights, air-
conditioning equipment, RF equipment or machines that create
electrical noise (e.g., vacuum cleaners).
Important:
1. If the unit’s enclosure appears disrupted or if all channel-
select LEDs flash continuously, please remove product
from service immediately and contact HSL Technical
Support at http://highseclabs.com/support/case/.
2. Do not connect product to computing devices:
a. That are TEMPEST computers;
b. That include telecommunication equipment;
c. That include frame grabber video cards
d. That include special audio processing cards.

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2-PORT SINGLE-HEAD SECURE KVM: SK21D-3 –DVI-I VIDEO, SK21P-3 –DISPLAYPORT VIDEO, SK21H-3 –HDMI VIDEO
Section 4 - Operation
Installation
1. Connecting devices to product console
Product requires connection of all displays; devices and computers
prior to powering it up.
Note: some devices such as user display would not be recognized if
connected after product is already powered up.
See figures above for connector locations.
Connect user display. Mark which display is coupled with which
computer. It is also recommended to mark which computer is
coupled with which channel.
Connect user keyboard and mouse to console keyboard and
mouse ports.
Connect headphones/speakers to console audio out port
(optional).
Notes:
1. Console USB keyboard and mouse ports are switchable, i.e. you
can connect keyboard to mouse port and vice versa. However,
for optimal operation it is recommended to connect USB
keyboard to console USB keyboard port and USB mouse to
console USB mouse port.
2. For security reasons products do not support wireless keyboards.
In any case do not connect wireless keyboard to product.
3. Non-standard keyboards, such as keyboards with integrated USB
hubs and other USB-integrated devices, may not be fully
supported due to security policy. If they are supported, only
classical keyboard (HID) operation will be functional. It is
recommended to use standard USB keyboards.
4. Console USB mouse port supports Standard KVM Extender
composite device having a keyboard/mouse functions.
2. Connecting the Computers
Using USB cables, connect each computer to the USB type B port
in "computer interface ports" area on product.
If computer uses audio output, e.g. speakers/headphones,
connect audio cable from its audio output port to the
corresponding audio input port on product.
3. Power up
Connect product DC power supply.
Power up user display/s. Select through display setup menu the
appropriate video input if applicable.
Power up the connected computers.
Power up the product.
When you power up your computers, product emulates display,
mouse and keyboard on each port and allows your computers to boot
normally. You should be able to move the mouse cursor on the
primary display connected to computer #1.
Check to see that the keyboard and mouse are working properly on
each computer.
Repeat this check with all occupied ports to verify that all computers
are connected and responding correctly.
If you encounter an error, check your cable connections for that
computer and reboot. If the problem persists, please refer to the
Troubleshooting section in this User Manual.

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2-PORT SINGLE-HEAD SECURE KVM: SK21D-3 –DVI-I VIDEO, SK21P-3 –DISPLAYPORT VIDEO, SK21H-3 –HDMI VIDEO
Section 4 - Operation
Typical system installation

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Section 4 - Operation
2-PORT SINGLE-HEAD SECURE KVM: SK21D-3 –DVI-I VIDEO, SK21P-3 –DISPLAYPORT VIDEO, SK21H-3 –HDMI VIDEO
Operation
Operating the Product
Self-Test Procedure:
As product powers-up it performs a self-test procedure. In case of
self- test failure for any reason, including jammed buttons, the
product will be Inoperable. Self-test failure will be indicated by the
following abnormal LED behavior:
All channel-select LEDs will be turned ON and then OFF;
A specific, predefined LED combination will be turned ON;
The predefined LED combination will indicate the problem
type (jammed buttons, firmware integrity).
Try to power cycle product. If problem persists please contact your
system administrator or technical support.
Now that product, computers and peripherals are connected and
powered up, it is ready for use.
Default Channel
After product boots up, the default active channel will be channel
#1. This will be indicated by white color illumination of
push-button #1.
Product Mapping to Sources
Product mapping to sources is indicated by stickers/labels specifying
which channel is mapped to which computer.
Front Panel Push-Buttons
Following power up, the default channel is #1.
The user can select any other channel by pressing the appropriate
front panel push button.
The mouse cursor will be positioned at the center of the selected
computer display. If computer is connected to multiple displays, the
cursor will be positioned at the center of the primary display.
The currently selected channel is indicated by white color
illumination of the appropriate push-button.
Once a different channel is selected - keyboard, mouse, and audio
follow selected channel, unless Freeze Audio functions has been
activated (see below for details).
Using "Audio Freeze" feature
Press "Freeze Audio" push button to lock audio to a specific channel.
The LED will indicate this option has been activated and to which
channel the Audio is locked to at the moment. This means that
switching channels would leave Audio active on current channel.
Restore-Factory-Default will release "Freeze Audio" function from
any channel it is locked to.

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Section 4 - Operation
2-PORT SINGLE-HEAD SECURE KVM: SK21D-3 –DVI-I VIDEO, SK21P-3 –DISPLAYPORT VIDEO, SK21H-3 –HDMI VIDEO
Keyboard Status Indication
In order to enhance usability, product provides keyboard status
indications via dedicated LEDs located on product front panel. To
maintain the required unidirectional connectivity between keyboard
and product, these indication are not given on the keyboard itself as
done with non-secure products
The keyboard status indications are given via 3 LEDs on the front
panel of the product:
• CL – CAPS Lock
• SL – SCROLL Lock
• NL – NUM Lock
The indications behave the same as the LEDs on the keyboard as if it
was connected directly to computer.
Switching from channel to channel may change the status of the
LEDs based on the current settings on the computer connected to
the active channel.