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790lA
A-26.
When more than one expander gate is used, the
gate outputs are connected as in parallel, as shown by the
dashed lines in figure A-S.
7900-112A
7900-113A
EXPANDED GATE
EXPANDER GATE
Figure A-7. Simplified Expander Gate
Logic Symbol
EXPANDED GATE
A - - - I
8 - - - 1
C - - - I
Figure A-S. Actual Expander Gate
Logic Symbol
A-27.
ENCODING GATE.
A-2S.
The encoding gate (figure A-9) has one input and
multiple outputs. When the input is high, all outputs (B, C,
and D) are high. When the input is low, the outputs are
either low or high, in accordance with the state of the logic
element to which each is connected.
A-29.
A typical circuit for an encoding gate is shown in
figure A-lO. With A high, all diodes conduct and all outputs
are clamped high. With A low, each diode is practically an
open circuit, and points B, C, and D assume the voltage level
of the circuit to which each is connected.
7900-114
7900-115
Logic Symbology
A~[~--+--)
:
Figure A-9. Three-Input Encoding Gate,
Logic Symbol
.. - - - - - 8
A----~~----~
"'---C
_------D
Figure A-lO. Typical Encoding Gate Circuit
A-3D.
MUL TIVIBRATORS.
A-31.
The multivibrators described here are of four main
types: flip-flops, Schmitt trigger circuits, one-shot multivi-
brators, and free-running multivibrators. All furnish a binary
output. However, unlike gate circuits, the duration of a
multivibrator output signal is not dependent on the dura-
tion of an input signal.
A-32.
The basic logic symbol for a multivibrator is a rec-
tangle as shown in figure A-l1. Letters in the symbol indi-
cate the type of multivibrator. The rectangle is divided hor-
izontally, with the upper portion representing the "set side"
and the lower portion representing the "clear side." The
multivibrator is considered set when the output from the set
side is high.
It
is considered cleared when the output from
the clear side is high. To avoid confusion, the symbol is
always oriented as shown in figure A-ll; inputs on the left,
outputs on the right.
SET SIDE
INPUTS
OUTPUTS
7900-116
Figure A-l1. Basic Logic Symbol Multivibrator
A-3
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