SECTION
4.
KEYBOARD
INTERFACE
The
HP
Vectra interface
to
its keyboard
is
through
an
HP-Human
Interface Link
(HP-HIL).
HP-HIL
is
the Hewlett-Packard proprietary
standard
for
interfacing one or more input devices
to
the system.
HP-HIL
provides
an
asynchronous serial communication protocol
that
enables the user
to
select a set
of
input devices (up
to
seven),
and connect them
to
the
HP
Vectra
without
purchasing additional
I/O
cards or using additional I/O slots. Cable management
is
simplified because the various input devices are "daisy-chained"
from the
HP
Vectra. The term daisy-chained refers
to
process
of
plugging the first input device into the
HP
Vectra, plugging the
second input device into the first, and
so
on.
The keyboard interface consists
of
two
blocks:
the
keyboard
controller, and the
HP-HIL
interface. This section will describe
these
two
blocks. Also included,
is
a cursory description
of
the
data
flow
necessary
to
receive a keycode from
the
keyboard and
to
send a command
to
the keyboard.
For
a detailed description
of
the keyboard interface refer
to
the
HP
Vectra
Technical
Reference
Manual
Volume 2: System
BIOS.
Keyboard Controller
The keyboard controller
is
an
8041 microcomputer (U87) which
has
been programmed
to
provide a communication path between
the
BIOS
and/or application programs and the
HP-HIL
subsystem.
It also provides three
output
lines and one input line
for
various
hardware system purposes. The 8041 provides
two
logical paths
for
communicating
with
the 80286: the application path and the
keyboard path.
Keyboard Interface 55
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