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PROCESSOR TECHNOLOGY CORPORATION
CUTS, COMPUTER USERS TAPE SYSTEM
SECTION V
1200 Hz represents a 11111 and one-half cycle of 600 Hz represents a
110
11 •
The output on pin 2 of U2 is applied to one section in U22
which provides sU'fficient current drive for the R15, 16 and 17 divi-
der network.
This divider and a jumper arrangement allow selecting
one of three outputs to be fed to the audio output jack *Jl-4 and
J2-4}.
The A-to-D jumper selects a 4-volt peak-to-peak square wave
output for a digital
recorder~
the A-to-B jumper selects a 270 mv
signal for the auxiliary input to an audio
recorder~
the A-to-C
jumper selects a 50 mv signal for
th~
microphone input to an audio
recorder.
5.3.4
Read Mode
When CUTS is in
ters oh Jl-2 and J2-2.
tive mixer (R3,4 and 6)
put of which is applied
amplifier U6.
the read mode, data from the recorders en-
These two inputs are mixed through a resis-
and fed to Ql, an emitter follower, the out-
to the negative input (pin 2) of operational
The first section of U6 is a high gain amplifier, with its
gain being determined by R9 and RIO.
The output from this amplifier
is coupled to the input (pin 6) of the following U6 stage and the
base of a Darlington pair (Q3 and 4) which provides high current
gain.
Current into the base of Q3 causes C29 to discharge.
(C29
charges through R25 to 5 V dc.)
The voltage on C29 in turn controls·
the gate of FET (field effect transistor) Q2.
Q2 functions as a
variable resistor which can be changed by its gate voltage.
Since
Q2 is connected between ground and the input network to the first U6
stage, it serves as a variable shunt.
A low gate voltage on Q2
decreases the shunt resistance and the input to u6.
In a like man-
ner, a high voltage on C29 results in an increased input to U6.
Q2,
3 and 4 with their associated circuitry, therefore, serve as an AGC
circuit which limits the input to the second U6 stage to approxi-
mately a 2 vol.t peak signal.
The second stage of U6 performs the needed audio to digital
conversion.
Feedback resistor R12, in conjunction with R13, esta-
blishes the level on the positive input (pin 5) of U6.
This level,
be it positive or negative, is the threshold which the negative
input (pin 6) must exceed in order for the output of U6 to switch
levels, positive to negative and the converse.
Since the feedback
loop is regenerative, U6 switches at its maximum rate, and u6
switches on each transition of the audio signal input.
It is in
this manner that U6 performs the audio to digital conversion.
The digital output of U6 is inverted in one section of U22
and applied to pin 2 of U19, an exclusive-OR gate which is connected
as a buffer without inversion.
If the output of U22 is low, the
V-8
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