Circuit
Description—7D14
TIME
BASE
AND CONTROL
CIRCUIT
General
The
Time
Base
and
Control circuit generates the control
signals
described in the Control
Signals discussion at the
start
of this
section. A
block diagram of the Time Base and
Control
circuit is shown in Fig. 3-16. This diagram shows
the
output signals produced
by this
stage and the basic
interconnections
between
blocks. The interconnections
shown
are intended only
to indicate interrelation
between
blocks;
and do not indicate a direct connection, or that
only a
single connection is
made between the given blocks.
Details
of the
inter-relation between stages in this
circuit
are
given in the circuit
description which follows. A
schematic
of
this circuit is shown on Diagram 5 in the
Diagrams
section.
Switch
Logic
The
outputs
from the Time Base and Control circuit
determine
the 7D14 measurement mode. These outputs are
a
function of
the MEASUREMENT INTERVAL,
REF
FREQ/CH
B,
RESET, and
Manual Gate Storage switches.
The
relationship between these switches and the stages in
the Time
Base and
Control circuit is as follows:
MEASUREMENT INTERVAL.
In
the
1
ms
through
10 s switch position,
the Gate Generator stage
GATE out
put
is controlled by one of the outputs of the Time Base
Decade
Counters stage. The switch position nomenclature
(e.g., 1
ms) refers to
the GATE output "on" time resulting
from
a
one-megahertz
reference-frequency input.
Also, in
these positions
the. selected gate is* connected to the
MONITOR
output connector
through the Gate Buffer.
In
the MANUAL GATE switch settings, the GATE out
put is
controlled manually by the ON and OFF push
buttons
through the Manual/External Gate Input stage.
When the
OFF button
is in, the GATE output can be con
trolled
by an external gating signal connected
to the EXT
GATE input connector.
REF
FREQ/CH
B.
In
the INT 1 MHz position, the
Divide
By Five Counter one-megahertz output is connected
to the Time Base
Decade Counters and
to the Reference
Frequency
Gate
stage.
Also, the Monitor Buffer
one-
megahertz
output
is provided to
the
MONITOR output
connector.
When
the EXT IN button is in, the EXT IN connector is
connected
to the Channel B
Input Shaper stage;
and, the
Channel B
Input
Shaper output
is provided to the Time
Base
Decade Counters and to the Reference Frequency
Gate stage.
RESET.
The
RESET pushbutton,
when pressed in,
grounds an input
to
the Reset
Input stage. This results in a
HI
RESET output. When the RESET button is
released, the
other
input
to
the Reset Input stage is
grounded. This
results in a LO
RESET output.
Manual
Gate Storage.
The Counter and
Readout
Encoding circuit
INTERNAL output
is connected to the
Display
Enable
stage through the off position of the Manual
Gate
Storage switch. When the INTERNAL input is HI,
the
switch
position has no effect on the Display Enable stage
DISPLAY
output. When the INTERNAL input is
LO, it can
be applied
to the Display Enable stage through the off posi
tion of the Manual
Gate Storage switch to
hold the DIS
PLAY output LO.
Block
Diagram Description.
The 5-MHz
Oscillator
is a
temperature-compensated
crystal oscillator.
The 5-MHz
output is
divided by the Divide by Five Counter stage to
provide
a
one-megahertz output to the Monitor
Output
stage and to the REF
FREQ/CH B switch.
The Channel B
Input Shaper shapes and amplifies signals
connected
to the
REF
FREQ/CH B EXT IN connector
when the EXT IN button
is in.
The
Time
Base Decade Counters count the reference fre
quency
selected
by the REF
FREQ/CH B switch, S50. This
stage consists
of seven
cascaded decade counters. Outputs
from
the
last
five
decade counters provide reference
frequency
division ratios of 103
, 104, 105, 106, and
107.
These
outputs are
selected by the MEASUREMENT
INTERVAL
switch
to provide a means of turning the Gate
Generator
on for precise time intervals. The time
intervals
selected are
the reciprocal of the divided reference
frequency
input. The
MEASUREMENT
INTERVAL switch
pushbuttons
are
labelled according to the time interval
selected for a
one-megahertz
reference-frequency input.
The Reset Input
stage produces the RESET signal to the
Gate Generator,
Display Enable, and DCU RESET Driver
stages
on command of the front-panel RESET pushbutton
or reset
signal
applied
to the pin-jack connector.
The
Manual/External
Gate Input stage
provides
outputs
to
the Gate Generator to turn the GATE
output on
or off
by
means
of the MEASUREMENT INTERVAL-MANUAL
GATE
pushbuttons, or by
means of an external gate signal
applied
to the EXT GATE connector.
The
Gate Generator stage generates the GATE control
signal.
The
complementary
GATE
and GATE outputs are
provided
to several stages within the Time Base and Control
circuit
and
to the Channel A Signal Conditioning circuit.
The
GATE "on" time is established by inputs
from
the
Time
Base Decade
Counters, Reference Frequency Gate,
and
Manual/External
Gate Input stages
as determined by
the
MEASUREMENT INTERVAL switch. The GATE "on"
time
can
be terminated by an input from
the Reset Input
stage. At
the end of
the GATE
"on" time, a CLEAR output
is provided
to the Display Enable stage. Also, an
output is
provided
to
the Lamp Driver to illuminate the GATE indi
cator
lamp
when the GATE
is "on".
3-19
Summary of Contents for 7D14
Page 4: ...7D14 ...
Page 11: ...Operating Instructions 7D14 Fig 2 1 7D14 front panel controls and connectors 2 2 ...
Page 33: ... 3 13 Fig 3 11 Logic diagram for Zero Cancel Logic stage Circuit Description 7D14 ...
Page 38: ...3 18 Fig 3 16 Time Base and Control circuit detailed block diagram Circuit Description 7D14 ...
Page 44: ...NOTES ...
Page 46: ...NJ Fig 4 1 Electrode configuration for semiconductors in this instrument I ...
Page 68: ...NOTES ...
Page 96: ... 7DI 4 DIGITAL COUNTER UNIT ...
Page 98: ...GRS 0371 BLOCK DIAGRAM ...
Page 99: ......
Page 103: ...0 0 I 200 mV 500 µs 0 001 200 mV 500 µs 0 001 MHz 00 mV E 00 µs 0 001 MHz ...
Page 106: ...1 ...
Page 110: ...A2 Logic Circuit Board Assembly jQ798i 798 jc743 CR744t uni R724 R742 JL744S FrR796 ...
Page 113: ......
Page 114: ...P 0 A2 LOGIC BOARD ...
Page 121: ... A B D t F H J NPR Tj ZWX V A AC M AEA HUM qAZ DEF HJ N P R S T J V V7X y ABM APAI AA 7DI4 ...
Page 129: ......
Page 130: ...4 7D14 DIGITAL COUNTER ...