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15.2.1
.1 0 Input/Output
Characteristics
All
digital inputs
and
outputs
are
interfaced
to 'B'
series CMOS logic,
which
operates
from
OV
/5V
sup-
plies. To
facilitate
interface with a
mechanical
switch,
some
inputs have
pull-up
or pull-down resistors.
15.2.1 .11
Miscellaneous
Front-Panel
Interconnections
The
Front-Panel
Interface provides
miscellaneous
in
te rconnections
between
t
he
fro nt
panel
and t
he
rest
of
the
system.
These
connections
come
from
t he
front
panel
through two
ribbon
cables
and
connectors,
J1
and .J2. They are
then
routed
through
edge connector
Pl.
15.2.2
ANALOG
INTERFACE
15.2.2.1 Input
Switching
(K2-K4,
02,
03,
06)
T he
input
to the
range
attenuator can
be selected
from
either
the EXT
INPUT
or
t he
INT SCOPE
TO
RNG
SW
inputs.
Ac
or
de
coupling may
be
selected for
the
external
input. Input
switching is
controlled
by the
DC
SELECT
and
EXT
I
NPUT SELECT
signals,
as
shown
in
Table
15-4.
T he
generation
of
these signals
is
discussed
in paragraph
15.2.1.4.
15.2.2.2 Range
Attenuator
(K5-K8, 04,
05,
07,
~
The
range
attenuator
provides
four
selectable val-
ues
of
attenuation:
X1,
X0.1,
XO.O
l
,
and
XO.OOl.
Attenuation
is
controlled
by
t
he
ATTEN
X0.001 to 1
signals, as
shown
in
Table
15-3.
Compensation
capac-
itor
Cll is adjusted
for maximum bandwidth. To
adjust
C1
1,
see
Section
3
on alignment.
15.2.2.3
Unity-Gain
Buffer Amplifier
Unity-gain
buff"er
amplifier
Qll
buffers
the signals
under
test
from
t he frequency-counter
pre-amplifier,
the DVM buffer amplifier,
and
the
scope's
vertical
pre-
amplifier
inputs.
R54 (coarse) and
R55
(fine)
are
adj
usted
so
t
hat t here
is
a voltage
gain
of one
from the
EXT
INPUT
to TPL To align R54 and
R55, see
Section
3
on alignment.
15.2.2
.4
Scope Vertical
Pre-Amplifier
(U3,
09,
01
3,
0 14)
The
scope's
vertical pre-amplifier
has
a
nominal
gain
of
fJO
when
the
front
panel's vertical-gain
potentiom-
eter
(which is connected
between
VERT GAIN
and
VERT GAIN
RETURN) is set to 0
ohms.
When the
gain
potentiometer
is set at 5K ohms,
the
gain of the
amplifier
is
less than or
equal
to 5.
The front
panel's
5K ohm vertical-position
potentiometer
(which
is
connected
between
VERT POSITION and ground)
varies the
de offset of t
he
amplifier.
This amplifier
drives
t he
VERT FROM
RNG SW output.
R19
and
R25
adjust t he gain
and
balance,
respectively,
of
the
vertical pre-amplifie r.
To
a lign
R19
and
R25, see
Section
3
on alignment.
Table
15-3
shows,
as a
function
of t he range-atten-
uator
setting,
t
he
vert
ical
pre-amplifier's
gain
from
the
selected
input to
the VERT
FROM RNG
SW output.
15.2.2.5
DVM
Buffer
Amplifier
The
DVM
buffer
amplifier
provides
switched- band-
width buffering
between
the
unity-gain
amplifier (Qll)
and the DVM circuitry
on
the Scope/DVM
Control
board(A
7).
In ac
mode,
operational
amplifier
U7 oper-
ates as a
unity-gain
amplifier
with a
gain
flatness of
±
2
percent out to 20
kHz.
In
de
mode,
analog switches
U6A and U6C
switch
C26 and
C22,
respectively,
into
the
amplifier
circuit.
In
this
configuration, t he
ampli-
fier
has a de
gain
of
1
and a
minimum
attenuation
of
30
dB
at
50
Hz. The
amplifier band wid
th
is
controlled
by
a
signal
from latch
U9,
which
has
the
opposite sense
of the DC SELECT
signal.
U4B inverts t he sense of
this signal
and
then translates it from
a
logic
level of 0
to
+5V
to
a logic level of
-8
to +8V.
The signal is
now
compatible wit
h
the
control
inputs
of U6A
and
U6C.
R41
is
adjusted
for a
gain
of one fro
m
TP1 to the
DVM
FROM RNG
SW output.
To adjust R41
,
see Section
3
on
alignment.
Table 15-3 shows
the
gain
from
the selected
input
to
the
DVM
FROM
R
NG SW
output
as a function of
the
range-attenuator
setting.
15.2.2.6
Frequency-Counter
Pre-Amplifier
The
frequency-counter pre-amplifier (Q12 and
U7)
converts
the output of
unity-gain
buffer
Qll
to
ECL
levels.
T he output
is differentially
connected through
the
EXT FREQ
CNTR and EXT
FREQ
CNTR
out-
puts
to the Processor
Interface
board (All}. Table
15-3 shows
the
sensitivity
of
this
amplifier
as
a
func-
tion
of
the
range
attenuator.
15.2.2.7 Scope
Horizontal
Pre-Amplifier
The
scope's
horizontal
pre-amplifier
provides
a
nominal voltage
gain
of
5
between the
HORIZ
INPUT
and the
HORIZ TO
SCOPE AMP output.
15-5
/( 15-6
blank)
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