Tektronix 7D14, Instruction Manual

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Circuit Description—7D14
The 7D14 Readout Encoding circuit consists of the
Digital-to-Analog (D-A) Converter, Over-range Indicator,
MEASUREMENT INTERVAL Switch Logic, Decimal
Logic, and Measurement Units Logic stages. The Readout
Encoding circuit encodes the Channel 1 and 2, Row and
Column output lines according to the format given in Table
3-1. A detailed block diagram of the Readout Encoding
circuit is shown in Fig. 3-13. A schematic of this circuit is
given on Diagram 4 in the Diagrams section.
Time-slot sequenced BCD data and zero-cancel logic out­
puts from the Counter circuit are applied to the D-A Con­
verter stage. The D-A Converter encodes the Channel 1 out­
puts for time-slot three through time-slot ten (TS-3 through
TS-10) as determined by the Counter circuit outputs.
During TS-3, TS-4, TS-5, and/or TS-6 the D-A Converter
can encode a SPACE instruction as determined by inputs
from the Counter circuit (Zero-Cancel Logic). A SPACE
instruction encoded in a time-slot results in a blank space
for the corresponding digit position.
TABLE 3-1
7D14 READOUT ENCODING FORMAT
Time-Slot
Number Description
Channel 1 Channel 2
TS-1 Determines decimal
position.
Encodes JUMP in­
struction in MANU­
AL GATE mode.
TS-2 Encodes to indi­
cate over-range
measurement.
Not used.
TS-3 Encodes most sig­
nificant (8th) digit
of measurement
(count) display, or
SPACE instruction.
Not used.
TS-4 Encodes 7th digit of
count display, or
SPACE instruction.
Encodes M (mega-)
and k (kilo-) pre­
fixes.
TS-5 Encodes 6th digit of
count display, or
SPACE.
Encodes H.
TS-6
Encodes 5th digit, or
SPACE.
Encodes z.
TS-7 Encodes 4th digit. Not used.
TS-8 Encodes 3rd digit. Not used.
TS-9 Encodes 2nd digit. Not used.
TS-10 Encodes 1st digit. Not used.
Time-slot pulse TS-2 from the oscilloscope readout
system is connected to the Over-Range Indicator stage. The
Over-Range Indicator stage encodes the Channel 1 outputs
for > (greater then symbol) on command of the OVER­
FLOW input.
The MEASUREMENT INTERVAL Switch Logic con­
nects time-slot pulse TS-1 to the Decimal Logic stage or to
the Measurement Units Logic stage. Also, the MEASURE­
MENT INTERVAL Switch Logic stage provides logic level
outputs to indicate the switch setting to the previously
mentioned stages and to the Time Base and Control circuit.
The INTERNAL output to the Time Base and Control
circuit indicates operation in the internal gate or MANUAL
GATE modes.
The Decimal Logic stage encodes the Channel 1 outputs
to determine the position of the decimal in the measure­
ment display. The Measurement Units Logic stage encodes
the Channel 2 outputs to display the proper measurement
units or the JUMP instruction as determined by the
MEASUREMENT INTERVAL Switch Logic outputs.
Digital-to-Analog Converter
Digital-to-Analog (D-A) Converter U560 produces an
output current which encodes the readout system Channel
1 Column output for time-slots TS-3 through TS-10. The
level of this output current is determined by inputs from
the Multiplexer, Time-Slot Inverters, and Zero-Cancel Logic
stages. During time-slots TS-3 through TS-6, the output
current encodes either decimal digits or a SKIP instruction
as determined by the Zero-Cancel Logic inputs.
Fig. 3-14 shows the input and output configuration of
U560. The output of U560 is a current into pin 15, shown
Fig. 3-14. Input and output configuration for U560.
3-15