HighSecLabs K304 User Manual page 16

When you power up your computers, the 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.
DPP Installation (Optional, K304E only)
The following process can be performed before or after power up.

If computer and KM Switch supports user authentication device,
connect another USB cable for the DPP function. DPP USB cable
can be connected to any free USB port in the computer.
Note: Do not connect DPP USB cable if user authentication device is
not needed. Secure KM Switch automatically detects this cable to
program DPP port selection logic accordingly.
If not all of the channels are having DPP function (some computers
not connected through DPP cable) – make sure that channel #1 is
using DPP – switch channels if needed.
When KM is powered on - once the connected device is qualified and
ready for use – the DPP status LED should illuminate green.
If connected device cannot be detected by the Secure KM Switch
then DPP status LED will not illuminate at all. Device must be fully
compliant with USB 1.1 or USB 2.0 standard.
15
4 & 8 port Secure KM Switch User Manual
Possible reasons:

Non standard USB device

Device only operating in USB 3 mode

Device not operating
Use other devices instead.
If the device is detected but does not match DPP qualification
specification – device will be rejected as indicated by status LED
illuminating steady red.