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NEGATIVE LOGIC LEVEL CONVERTER PAC, MODEL LC-335
The Negative Logic Level Converter PAC, Model LC-335 (Figures A-92 and
A-93), contains 10 independent converter circuits.
The N-input accepts a negative logic
signal (i.e., logic ONE is a negative voltage) for conversion into a standard
µ-PAC
posi-
tive logic signal.
The µ-input uses a
µ-PAC
signal to control or gate the negative logic
signal.
When the circuit is enabled, there is no logic inversion from the converting input
to the output.
The operation of the circuit is summarized in Tables A-3 and A-4.
Table A-3.
Logic Truth Table
Negative
Positive
Logic
Logic
N
µ
Output
0
0
1
0
1
0
1
0
1
1
1
1
0. Ov to -1. 5v
For the N -input:
Logic ZERO
Logic ONE
-2. 8v to - l 5v (or not connected)
For the µ-input:
Logic ZERO
=
O. Ov to +l. 2v
CIRCUIT FUNCTION
=
+3. Ov to +6.
3v
(or nut connected)
Table A-4.
Voltage Truth Table
(With Nominal Voltages)
N
µ
Output
Ov
Ov
+6v
Ov
+6v
Ov
-6v
Ov
+6v
-6v
+6v
+6v
Each level converter consists of a standard NAND gate microcircuit and a level
shifter.
The converting input (N) drives the emitter of a common base transistor whose
base is referenced to -2v.
When a logic ZERO (Ov) is applied to this input, the emitter of
transistor Ql becomes more positive than the base and Ql is turned off.
This is inter-
preted as a logic ONE at the NAND gate input.
When the converting input is a ONE (negative
voltage or not connected), Q 1 is turned on, causing the NAND gate output to be +6v.
A-161
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