5-4
Chapter 5: 5953 USB DynaKey Migration
Hot Plug
The
NCR
5953
USB
DynaKey
is
hot
‐
pluggable
.
That
is,
both
the
DVI
and
USB
connections
may
be
disconnected
and
the
DynaKey
replaced
without
removing
power
from
the
terminal.
The
Wedge
DynaKey
cannot
be
removed
or
replaced
without
removing
power
from
the
terminal.
POS-Checkout Style Keyboard
The
greatest
difference
between
the
NCR
Wedge
DynaKey
and
the
USB
DynaKey
is
the
communications
between
the
keyboard
and
the
host
computer.
The
Wedge
DynaKey
communicates
using
the
PS/2
communications
protocol,
which
is
bit
‐
serial
and
operates
at
approximately
25Kbps.
The
USB
DynaKey
uses
the
USB
1.1
protocol,
which
is
a
newer
and
different
bit
‐
serial
protocol
that
operates
at
either
1.5
or
12Mbps.
The
keyboard
operates
at
12Mbps.
Furthermore,
each
of
these
protocols
includes
a
software
layer.
The
PS/2
software
layer
is
very
simplistic,
and
presents
a
challenge
when
adding
additional
capabilities
beyond
the
keyboard
itself.
All
the
added
devices,
such
as
MSR,
Keylock,
tone,
and
scanner
are
implemented
as
wedge
devices.
That
term
means
that
these
devices
are
wedged
into
the
keyboard
data
stream
and
must
spoof
their
way
past
the
O/S
to
transfer
data.
This
technique,
though
widespread,
can
have
problems,
and
is
not
standardized.
The
USB
software
layer
is
standardized
and
richly
defined.
It
supports
multiple
simultaneous
channels
of
communications,
and
allows
additional
capabilities
to
be
added
without
negative
impact.
