Tektronix 7834

1988-53
Figure
3-28 . Typical readout display where only Channel 2 of the
Right
Vertical and B Horizontal units is displayed .
locations in the
Matrix (shaded area) are available for future
expansion of the Readout System .
The method of address-
ing the locations in the Character
Selection Matrix is
described in the following discussion .
Developing
the Display
The
following basic description of the Readout System uses
the block diagram
shown in Figure 3-29 . This description is
intended to
relate the basic function of each stage to the
operation of
the overall Readout System . Detailed informa-
tion on circuit
operation is given later .
The key block in
the Readout System is the Timer Stage .
This stage
produces the basic signals that establish the tim-
ing sequences
within the Readout System . The period of the
timing signal is
about 250 microseconds (drops to about
210 microseconds
when Display-Skip is received ; see detail-
ed description
of Timer stage for further information) . This
stage also produces
control signals for other stages within
this circuit and interrupt
signals to the Vertical Amplifier,
Horizontal Amplifier,
and Logic circuits, which allow a
readout display
to be presented . The Time-Slot Counter
stage receives a
trapezoidal voltage signal from the Timer
stage and directs
it to one of ten output lines . These output
lines are labeled TS-1 through
TS-10 (time-slots 1 through
10) and are connected to the vertical
and horizontal plug-in
compartments as well as to various
stages
within
the Read-
out System . The output lines are energized sequentially,
so
there is a pulse on only one of the 10 lines during any
250
microsecond
timing period . After the Time-Slot Counter
stage has counted
time-slot 10, it produces an End-of-Word
pulse which advances the system
to the next channel .
Two output lines (row and column) are
connected from
each channel of the plug-in unit back
to
the
Readout Sys-
tem . Data is typically encoded on these output lines by
connecting resistors between them and the time-slot input
lines
.
The
resultant output is a sequence of 10 analog
current levels
that
range
from 0 to 1 milliampere (100 mi-
croamperes/step)
on the row and column output lines . This
row
and column correspond to the row and column of the
Character Selection Matrix in Figure 3-27 . The standard
format for encoding information onto the output lines is
given in
Table 3-4
.
(Special-purpose plug-in units may have
their own
format for readout ; these special formats will be
defined in the manuals for these units .)
The
encoded column and row data from the plug-in units is
selected by
the Column Data Switch and Row Data Switch
stages respectively . These stages take the analog current
from the
8 data lines (2 channels from each of the 4 plug-in
compartments)
and produce a time-multiplexed analog volt-
age output containing all
of the column and row informa-
tion from the plug-ins . The
Column and Data Switch and
Row Data Switch are sequenced by
the
binary Channel
Address Code from the Channel Counter .
The time-multiplexed output of the Column Data Switch is
monitored by the Display-Skip Generator to determine if it
represents valid information
that should be displayed . When-
ever information is not encoded
in a time-slot, the Display-
Skip Generator produces
an output level to prevent the
Timer stage from producing the control
signals that normal-
ly interrupt the crt display and present a character .
- Time-Slot Number
TS-1
TS-3
~TS-4
TS-5
TS-6
TS-7
TS-8
-_-
TS-9
TS-10
TABLE 3-4
Standard Readout Format
Theory of Operation-7834
Description
Determines Decimal
Magnitude
(num-
ber
of
zeros
displayed or prefix change
information)
or the
IDENTIFY
func-
tion (n
o d
ispl
a y during this time-slot) .
Indicates normal
or inverted
input
(no
display for no rmal) .
Indicates calibrated
or uncalibrated
condition of plug-in
variable control
(no display for
calibrated condition)
.
Not encoded by plug-in unit . Left
blank to allow addition of zeros by
Readout System .
Defines
the prefix which modifies the -
units of measurement
.
Defines
the units of measurement of
the plug-in unit . May be standard unit
of measurement (V, A, S, etc .) or spe-
cial units selected from the Character
Selection Matrix .
Scaling . ~~~_`~
3-
3 7