Tektronix 7834

Theory of Operation-7834
Decimal-Point Character
The Decimal-Point Character address (see Fig . 3-27) allows
a decimal point to be encoded for special formats .
This
decimal point can be placed in any character position
by
encoding column 9 with row 8 during the corresponding
time slot . The application of row 8 data to the X and
Y
input of the Format Generator through R3478 and
R3479
respectively, provides horizontal and vertical
positioning
current for the decimal points .
Format Generator
The
X-
and
Y-deflection signals produced by the Character
Generator stage are
connected
to
pins 2 and 7, respectively,
of the Format Generator (03480) . The
Channel Address
Code from the Channel Counter is also
connected
to
pins 1,
8, and 15 of this stage .
The Channel Address Code directs
the Format Generator to add
current
to
the X and Y signals
to deflect the crt beam to the area of the
crt associated with
the plug-in channel that originated the
information (see
Fig . 3-26) . The Channel Address Code
and the resultant
word positions are shown in Table 3-5 .
The Ready signal at
pin 13 (coincident with the Vertical and
Horizontal Off
Command output) activates this stage
when
a character
is
to be displayed on the
crt
.
Resistors R3466 and R3468
determine the horizontal and vertical size, respectively, of
the displayed characters
.
The character position current
from the Decimal Point Logic and Character Position Coun-
ter stage is added to the X (horizontal) input signal to space
the characters horizontally on the crt (see previous
discussion) .
3-
5
0
DECIMAL-POINT LOCATION ENCODED
DURING THIS TIME-SLOT -- NO
DISPLAY
ALWAYS
SKIPPED
EVEN IF
NO DATA
ENCODED
7
~1
.11 .FJ
DECIMAL POINT
LOCATION NO . 3
(COLUMN
3)
FIRST POSSIBLE CHARACTER DIS-
PLAYED ON CRT AT THIS LOCA-
TION
DECIMAL POINT
LOCATION NO . 4
(COLUMN 4)
DECIMAL POINT
LOCATION NO . 5
(COLUMN 5)
Y-Output Amplifier
The Y-output signal at pin 6 of Format Generator U3480 is
connected to the Y-Output Amplifier 03486 and
03493 .
This stage provides a low impedance load for
the Format
Generator while providing isolation between the
Readout
System and the driven circuits . Vertical Separation adjust-
ment R3490 changes the gain of this stage to control
the
vertical separation between the readout words displayed
at
the top and bottom of the graticule area .
X-Output Amplifier
The X-Output Amplifier 03489 and
03499 operates like
the Y-Output Amplifier, to
provide the horizontal deflec-
tion from the readout signal available at
pin 4 of 03480 .
The gain of this stage is fixed by the
values
of
the resistors
in the circuit .
Display Sequence
Figure 3-39 shows a flow chart for the Readout System
.
This chart illustrates the sequence of events that occur
in
the Readout System each time a character is
generated and
displayed on the crt .
FIRST NUMBER OF MEASUREMENT
NORMALLY DISPLAYED AT THIS
LOCATION
DECIMAL POINT
LOCATION NO . 6
(COLUMN 6)
DECIMAL POINT
LOCATION NO . 7
(COLUMN 7)
1195-37
Figure 3-38 . Readout word relating 10 possible character locations to the decimal point instructions that can be encoded, and
the resultant crt
display .