I
Momentary Key Operation
Momentary control keys do
not
provide a coded
output
to
the interface
bit
lines,
but
do activate a control line to the
keyboard interface. The momentary key interposer, unlike
the latch key interposer, has a link (Figure 1-6) that operates
on the latch spring, and the pivot hole
is
not elongated.
As the key
is
pressed, the <lobber moves the interposer
down, causing the link
to
pivot (Figure 1-6). The latch
spring closes the EDS
as
it follows the arc
ot
the link
(Figure 1-7). The interposer
is
not
latched down by the
latch spring, and the using system determines
if
a keyboard
restore cycle occurs
as
a result
of
pressing a momentary
key. The circuit through the EDS remains closed
as
long
as
the key
is
held down.
When the key
is
released, the interposer
is
restored
by
its
return spring and the link cams the latch spring away from
the EDS.
Typamatic Key Operation
When a typamatic key
is
held down with a slightly more
than
normal pressure, it permits automatic repetition
of
a
graphic, space,. or function key. Normal pressure
on
the
key causes only one operation,
as
with
a standard latch-
type key.
The typamatic keylever (Figure 1-8) has a typamatic
latch pivoting
on
the keylever at the front. When the
keylever
is
pressed, the typamatic latch downstop strikes
the
top
of
the interposer fulcrum. This
is
the normal stop
for
the
typamatic keylever, and actions
of
the <lobber,
interposer, and switch are identical to a standard latch key
Figure 1-6. Momentary Key (Normal Position)
1-4
(3/71)
mechanism. Additional pressure
on
the keylever overcomes
the typamatic latch spring tension, causing the latch to
pivot downward from the keylever. The turned-over ear
on the typamatic latch then strikes the
top
of
the interposer
projection, and holds the interposer down in the latched
position. When the restore magnet
is
de-energized during
this cycle, the restore bail moves the interposer to the front.
The turned-over ear pivots down behind the interposer
projection (Figure 1-9) and holds the interposer forward.
The interposer remains in this position, with the EDS closed,
until the key
is
released. Data
is
sampled
by
the system
until the interposer
is
restored and the EDS switch opens.
When the keylever
is
released, the interposer restores
immediately. The interposer return spring pulls the inter-
poser to the rear
of
the keyboard, where
it
strikes the latch
spring and allows the switch
to
open. The electronic circuits
complete the keyboard cycle
that
may already be in progress
by providing proper timing for the data lines and the
'data
available' signal (refer to the timing chart for the 5475 in
Appendix A).
Another method can begin a typamatic operation.
If
the keylever
is
not
pressed to its limit soon enough, a full
restore cycle occurs. The <lobber
is
out
of
position because
the keylever
is
down.
If
the keylever
is
pressed to its limit
at this time, the turned-over ear
of
the typamatic latch will
strike the interposer projection. The interposer will move
down and latch under the latch spring. As the restore
portion
of
the cycle begins, the interposer will again move
behind the turned-over ear
of
the typamatic latch and will
be held in this position until the key
is
released. The
remainder
of
the operation
is
the same
as
the first repeat
operation described.
