Operating instructions

CHAPTER 2 TECHNICALLY SPEAKING

when the user presses a key for On Screen Display commands. Some processors can even update the

NumLock, Scroll Lock, and Caps Lock status lights on the keyboard for the currently active computer.

 Video, such as the multiscan monitor. Most switches support a scan function, which causes the switch to

sequentially and incrementally display the video from each connected computer. Most also provide a

broadcast function that sends data to all the attached computers simultaneously.

Multiple platform and multiple user KVM switch processors require further firmware coding. These switches

must act as translators between the switch and the different platform computers attached to it. The

transparency of the transition from one platform to another depends on the engineering design.

Keyboard and Mouse Signal Recognition

Keyboards and mice from the three platforms (PC, Sun and Mac) are not compatible. If your computer

configuration contains only one platform, your KVM switch selection is simple: a single platform switch

meets your needs. However, users who have two or more platforms connected to the KVM switch will need a

multiple platform switch that can recognize the different types of computers and signals.

Keyboard Technology

While keyboards for all three platforms are similar and look about the same (generally 85 or 101 keys), the

technical working of each platform differs.

• The signals to and from the keyboard travel in 8-bit serial data streams.

• Scan codes tell the computer what key (or combination of keys) is depressed and when it is released.

The BIOS (whether keyboard or main) translates the scan codes into American Standard Code for

Information Interchange (ASCII), which lets KVM technology use any key combination desired to

initiate tasks.

That’s about the last of the similarities of the keyboards across different platforms.

Personal Computers (PCs) need constant communication with the keyboard. If the computer sends out a

signal to ensure the keyboard is still present and functional, but does not receive a response, the PC may

freeze, or in a worst case scenario, crash. To avoid this problem, the solution is a dedicated processor KVM

switch configuration.

Macintosh computers use a separate bus for keyboard signals, but it also carries the mouse signals and other

peripherals.

Sun technology is similar to Macintosh in appearance only. The mouse plugs into the keyboard, which then

plugs into the computer.

There are differences between the keyboard platforms. NTI provides keystroke translation for multiple

platform switches. Sun keyboards have 14 extra keys not found on PS/2 101, Win95 and Apple Extended

keyboards. NTI offers a keystroke emulation chart for those extra keys, as well as a chart of emergency

start-up keys for Sun keyboards.

NTI has the appropriate keyboard connectors for your configuration – NTI products let you use your

keyboard of choice, no matter what platform you use. For example, if a user prefers the PS/2 keyboard and

attaches SUN or MAC computers to the KVM switch, he or she can use that PS/2 keyboard for all

platforms. The NTI KVM switch properly translates the signals for each platform as necessary.

There are differences between the keyboards for different platforms. NTI provides keystroke translations for

multi-platform switches. Table 1 identifies the characters and their equivalent keystrokes across the various

platforms.