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6 External Keyboard
An external keyboard may be connected directly to the Braille System. Keyboards of any
make or model may be used, provided they comply with the following requirements:
๏ท AT keyboard
๏ท PS2 connection
๏ท low current consumption (recommended 30 mA with LEDs turned off)
The external keyboard transmits your key strokes to the Braille System in the same way as
the internal Braille keyboard. You can therefore operate both an external and the internal
keyboard in parallel. Please refer to Chapter "Installation" for the procedure for connecting
an external keyboard.
Please remember that all the information described in this section applies only to an
external keyboard, not to the built-in Braille keyboard.
6.1 General
Any keyboard transmits encoded data indicating which key has been pressed or released.
These data do not in themselves contain any information about what this key stroke
means, i.e., which character it should generate. That information is assigned by the so-
called keyboard driver, and depends on the desired language. This means, for example,
that if a U.S. English keyboard layout has been selected, the character ":" is realized by
pressing "Shift รถ" on a German keyboard.
Depending on the language (which means on the keyboard layout currently in force), the
Braille System's keyboard driver needs further information indicating how it is to implement
the encoded key stroke information. Therefore a table for assigning key strokes to
characters must be present in the Braille System, the keyboard layout table.
The Braille System already contains a fixed, programmed keyboard layout table for a
German keyboard, as well as a downloadable keyboard layout table. This table is called
"kbdlyout.hsf" for all languages. The internal keyboard layout table is always activated
when no downloadable keyboard layout is found. This is the case, for example, when no
files at all are stored on the media after the Braille System has been reformatted. When
the Braille System is turned on, it checks whether an error-free, downloaded table is
present: if not, it generates the warning message
'Warning: No keyboard layout file found. Using standard layout.'
and switches automatically to the default internal table. The warning is even generated
when no external keyboard is connected to the Braille System, because in this case it is
still possible to attach the keyboard later.
The keyboard layout table appropriate to your country is already loaded into the Braille
System for shipping. However, you can also modify this file, or create a new one and then
load it into the Braille System. This means that the existing keyboard layout will be
overwritten.
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