Tektronix 7834

by the plug-in unit along
with
row
3 during time-slot 1, the
Zeros Logic and Memory produces
a negative-going output
pulse at pin 1 to switch the Column
Data Switch and Row
Data Switch to the ninth channel . Then, time-slot pulses 2
through 9 encode an output current through resistors
R3242 and 83248 for column data and
83251 and 83258
for row data . This
provides the current necessary to display
the word IDENTIFY in
the
word
position allotted to the
channel that originated the Identify command
.
After
com-
pletion of this word, the Column
Data
Switch and Row
Data Switch continue with the next word in the
sequence .
The Word Trigger signal from the Word Trigger stage is
connected
to pin 9 of U3401 through C3401 . At the end of
each
word of readout information, this pulse goes LO . This
erases the four
memories in the Zeros Logic and Memory in
preparation for the
data to
be received from
the next
channel .
Character Generator
The
Character Generator stage consists of five similar inte-
grated circuits (U3461
through U3469), which generate the
X (horizontal)
and
Y
(vertical) outputs at pins 16 and 1,
respectively,
to produce the character display on the crt .
Each
integrated circuit can produce 10 individual characters ;
U3461 (designated
"Numerals") can produce the numerals
0 through 9 shown in row
1 of the Character Selection
Matrix (Fig . 3-27) . Integrated circuit
U3463 can produce
the symbols shown
in row 2 of the Character Selection
Matrix and U3465 produces the prefixes and some letters,
used
as prefixes, shown in row 4 . Integrated circuits U3467
and U3469 produce the remaining letters shown in rows 5
and 6
of
the
Character Selection Matrix .
All
of the Character Generator stages receive the Column
Digital Data from
the
Column
Decoder U3418 in parallel .
However, only one
of the Character Generators receives row
data at a particular time, and only
the stage receiving this
row data is activated . For example, if column 2 is encoded,
the five character Generators are enabled so that either a
1, >, Ft, V, or an N can be produced . If row 4 has been
encoded at the same time, only the Prefix Character Gener-
ator
U3465 will produce an output to result in a "F .c" being
displayed . The
activated Character Generator provides
current
output
for the
Format Generator to produce the
selected character
on the crt . In a similar manner, any of
the characters shown in the
Character Selection Matrix can
be displayed by correct addressing
of the row and column .
Decimal Point Logic and Character Position
Counter
Decimal Point Logic and Character Position Counter U3470
performs two functions . The first function is
to add
a
stair-
Theory of Operation-7834
case current to the
X
(horizontal) signal to space the
characters horizontally
on the crt .
After
each character is
generated, the negative-going edge of the Ready signal at
pin 5 advances the Character Position Counter
.
This
pro-
duces a current step output at pin 3 which, when added
to
the X signal, causes
the next character to be displayed one
character space to the right . This stage can also be advanced
when
a Space instruction is encoded so a space is left be-
tween the displayed
characters on the crt . Row 10 informa-
tion from the Row
Decoder is connected to pin
4
of U3470 .
When row
10 and column 0 are encoded, the output of this
stage
advances one step to move the next character another
space
to
the
right . However, under this condition, no dis-
play is produced on the crt during this time-slot, since the
Character Generators are not activated .
Time-slot
pulses
1, 2, and
3 are also connected to pin
4
of
U3470 through VR3470, VR3471, and VR3472 respec-
tively and 83470, R3472 and 83473 . This configuration
adds
a space to the displayed word
during
time-slots 1,
2,
and 3 even if information is not encoded for display during
these time-slots . With this feature, the information display-
ed during time-slot 4 (scaling data) always starts in the
fourth character position whether data has been displayed
in the previous time-slots or not . Therefore, the resultant
crt display does not shift position as normal-invert or cal-
uncal information is encoded . The Word Trigger pulse
connected to pin 8 resets the Character Position Counter to
the first character position at the end of each word .
The
Decimal Point Logic portion of
this stage
allows
decimal points to be added to the crt display
.
In accordance
with the Standard Readout Format, row 7 encoded coinci-
dent with columns 3 through 7 addresses
a decimal at one
of five locations (identified in row 7
of
the Character Selec-
tion Matrix, Fig . 3-27) . This instruction refers to the deci-
mal point location in relation to the total number of
characters possible in one word (see Fig . 3-38) . For example,
column 3 encoded with row 7 during time-slot 1 places a
decimal
point in location No . 3 . As shown in Figure 3-38,
this displays a decimal point
after the third character that
can be displayed on the crt
. (The first three time-slots pro-
duce a space whether
data is encoded or not ; see previous
paragraph .)
When
decimal-point data is encoded, the crt is unblanked so
a readout display
is presented . Since row 7 does not activate
any of the five Character
Generators, the crt beam is de-
flected vertically by the
application of row-7 data to the
Y
input of the Format Generator through
83477
.
This places
the decimal point between
the characters along the bottom
line of the readout word . After
the decimal point is pro-
duced in the addressed location,
the crt beam returns to the
location indicated by the Character Position
Counter to
produce the remainder of the display
.
3- 49