Philips PM 3266 - 3.2.8. Storage Section

3.2.8.
Storage
Section
3
.
2.
8.
1. In
traduction
See Fig.
3.62.
for
the
circuit
diagram.
The first
part
of this
description
deals
with
the
functioning
of the
separate
blocks
mentioned
in the
block
diagram
description
and
explains
the
operation
of each
circuit
block
under
various
conditions
and
modes.
The
second
part
of
this
description
explains
how
the various
pulses
are
generated
that
control
the
c.r.t.
storage
electrodes
in
the
WRITE,
FAST,
STORE
and
NON
STORE
modes.
The
pulses
generated
in
these
modes
are
traced
through
the
circuit
blocks
that are
described
in
the
first
part
to show
how the
various
waveforms
on
the
c.r.t. storage
electrodes
are
derived.
The
storage
section
of
the
oscilloscope
comprises
the following
circuit
blocks;
—
Pushbutton
switch
decoder
—
Timer
—
Auto-erase
timer
—
Dual oscillator
—
ETB and
BTB
pulse
generator
—
Stabilisation
pulse
generator
—
Miscellaneous
logic
elements
—
Quad
bilateral
switches
D2401,
D2402,
D2403
—
Storage
amplifiers.
The logic
circuits
are of the
LOCMOS
type, which is
highly
sensitive
to static
discharges.
An explanation is
considered
necessary
for personnel
who have had
no handling
experience
with
these
devices.
HANDLING
LOCMOS
DEVICES
The word LOCMOS
is the
abbreviation for
Local
Oxidation
Complementary
Metal
Oxide Semiconductor,
which
indicates
that
field-effect transistors
with an insulated
gate
are
used in this type
of logic.
Although
these field-effect
transistors
have input protection
diodes, this
type of logic is sensitive
to electro-
static charges.
To safeguard
against
any possible damage
to the LOCMOS
circuits, the following
rules
must be observed:
a.
Store and transport
the circuits
in their original
packing, which
short-circuits
the leads or
insulates them
from
external
influences.
b.
Electrically
connect together
to the
same potential:
testing or handling
personnel,
measuring
equipment,
soldering
iron
and circuit
board with the
LOCMOS circuits
being handled.
This
potential
can, of
course, be
earth.
c. After
the LOCMOS
circuits have
been mounted on
the board,
proper handling
precautions
should still
be
observed.
Until the
subassemblies are
inserted
into a complete system
in which
the proper
voltages
are
applied,
the board
is no more than
an extension
of the leads of
the device
mounted
on the board.
To
prevent
any static discharges
from
being transmitted through
the
board wiring
to the device,
it is
recommended
that conductive
clips or conductive
tape
be put in the circuit-board
terminals.
d. To prevent
permanent
damage due
to transient voltages,
do not insert or
remove
LOCMOS
devices, or
printed-circuit
boards
containing
LOCMOS devices, from
test sockets
or systems
with
power on.
e.
Flandling
personnel should
be dressed
in clothing of
non-electrostatic
material (i.e. no wool, silk
or
synthetic fibres).
3
.
2. 8
.
2.
Functioning of the storage system.
PUSHBUTTON
SWITCH DECODER
The
pushbutton
switch decoder circuit
decodes the
position of the pushbuttons
FAST,
WRITE and STORE
(S24C, S24B,
S24A respectively).
If the
WRITE
and STORE
pushbuttons
are depressed together
the
MEMORY
OFF
(NON-STORE) function
is selected.
If
a
faulty
pushbutton
combination
is chosen then the
STORE mode
is automatically
selected.
The
decoder has eight
logic
output
conditions:
FAST, WRITE,
STORE
and
NON-STORE
(MEMORY
OFF),
which
are high if
the corresponding
function
is selected,
and the four
inverse
states of
these
outputs. These
logic outputs
are available
from
the
quadruple flip-flop
D2204.