Tektronix 7623, Instruction Manual

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Circuit Description— 7623/R7623 Service
NOTE
Logic symbols used on the diagrams depict the logic
function and may differ from the manufacturer's
data.
Logic Polarity
All logic functions are described using the positive logic.
Positive logic is a system of notation where the more positive
of two levels (HI) is called the true or 1-state; the more
negative level (LO) is called the false or 0-state. TheHI-LO
method of notation is used in this logic description. The
specific voltages which constitute a HI or LO state vary be­
tween individual devices.
NOTE
The HI-LO logic notation can be conveniently con­
verted to 1-0 notation by disregarding the first letter
of each step. Thus:
HI = 1
LO = 0
Wherever possible, the input and output lines are named
to indicate the functions that they perform when at the HI
(true) state. For example, the line labeled, "Display B
Command" means that the 8 Time-Base unit will be
displayed when this line is HI or true. Likewise, the line
labeled "X-Compensation Inhibit" means that the X-
Compensation function is inhibited or disabled when this
line is HI.
Input/Output Tables
Input/output (truth) tables are used in conjunction with
the logic diagrams to show the input combinations which
are of importance to a particular function, along with the
resultant output conditions. This table may be given either
for an individual device or for a complete logic stage. For
examples of input/output tables for individual devices, see
Table 3-1.
Non-Digital Devices
It should be noted that not all of the integrated circuit
devices in this instrument are digital logic devices. The
function of non-digital devices will be described indi­
vidually using operating waveforms or other techniques to
illustrate their function.
MAIN INTERFACE
Diagram 1 shows the plug-in interface and the intercon­
nections between the plug-in compartments, circuit boards,
etc. of this instrument.
LOGIC CIRCUIT
The Logic Circuit develops control signals for use in
other circuits within this instrument and in the associated
plug-in units. These output signals automatically determine
the correct instrument operation in relation to the plug-in
installed and/or selected, plug-in control settings, and the
7623 control settings. A schematic of this circuit is shown
on diagram 2 at the rear of this manual.
Logic Block Diagram
A block diagram of the Logic Circuit is shown in Fig.
3-2. This diagram shows the source of the input control
signals, the output signals produced by this circuit, and the
basic interconnections between blocks. The interconnec­
tions shown are intended only to indicate inter-relation
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-relationship between stages
within this circuit are given in the circuit description which
follows.
The operation of each of these stages is discussed
relating the input signals and/or levels to the output, with
consideration given to the various modes of operation that
may affect the stage. A logic diagram is also provided where
applicable. These diagrams are not discussed in detail, but
are provided to aid in relating the function performed by a
given stage to standard logic techniques. It should be noted
that these logic diagrams are not an exact representation of
the circuit but are only a logic diagram of the function
performed by the stage. An input/output table is given,
where applicable, for use along with this circuit description
and logic diagram. These input/output tables document the
combination of input conditions which are of importance
to perform the prescribed function of an individual stage.
Z-Axis Logic
The Z-Axis Logic stage produces an output current
which sets the intensity of the display on the CRT. The
level of this output current is determined by the setting of
the front-panel INTENSITY control, an external signal
from the rear panel EXT Z AXIS input connector, or
signals from the plug-in compartments. The Vertical
Chopped Blanking from (J55 is applied to this stage to
blank the CRT display during vertical trace switching. The
Intensity Limit input from the horizontal plug-in compart­
ment provides protection for the CRT phosphor at slow
sweep rates.
The Z-Axis Logic stage consists of transistor 108,
dual-transistor Q90 and integrated circuit U99, which is a
five-transistor array. A simplified schematic of the Z-Axis
3-6