Tektronix 7623, Instruction Manual

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Circuit Description— 7623/R7623 Service
from m (100 microamperes column current; column 1) to
no prefix (zero column current; column zero) so only the
unit of measurement encoded during time-slot 9 is dis­
played. Notice that reducing the prefix program from
column 1 to column 0 programs the Readout System to not
display a character at this readout location.
A further feature of the Zeros Logic and Memory is the
Identify function. If 10 units of column current are
encoded 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 which switches 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 R2191-R2199 for column
data and R2201-R2209 for row data. This provides the
currents necessary to display the word IDENTIFY on the
CRT in the word position allotted to the channel which
originated the Identify command. After completion 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 U2232 through C2242. 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 Generators
The Character Generator stage consists of five similar
integrated circuits U2270, U2272, U2274, U2276, and
U2278, which generate the X (horizontal) and Y (vertical)
outputs at pins 16 and 1 respectively to produce the
character displayed on the CRT. Each integrated circuit can
produce 10 individual characters. U2270, which is desig­
nated as the "Numerals" Character Generator, can produce
the numerals 0 through 9 shown in row 1 of the Character
Selection Matrix (Fig. 3-24). U2272 can produce the
symbols shown in row 2 of the Character Selection Matrix
and U2274 produces the prefixes and some letters of the
alphabet which are used as prefixes in row 4. U2276 and
U2278 produce the remaining letters of the alphabet shown
in rows 5 and 6 of the Character Selection Matrix. All of
the stages receive the column digital data from Column
Decoder U2244 in parallel. However, only one of the
character generators receives row data at a particular time;
only the stage which receives both row and column data is
activated.
For example, if column 2 is encoded by a plug-in
unit, the five Character Generators are enabled so that
either a 1, < µ, V, or an N can be produced. However, if at
the same time row 4 has also been encoded by the plug-in
unit, only the Prefix Character Generator U2274 will
produce an output to result in a µ displayed on the screen.
This integrated circuit provides current outputs to the
Format Generator which produce the selected character on
the CRT. In a similar manner, any of the 50 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
The Decimal Point Logic and Character Position Counter
stage U2260 performs two functions. The first function is
to produce a staircase current which is added 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 produces a current step
output at pin 3 which, when added to the X signal, causes
the next character to be produced one character space to
the right. This stage can also be advanced when a Space
instruction is encoded by the plug-in unit so that a space is
left between the displayed characters on the CRT. Row 10
information from the Row Decoder is connected to pin 4
of U2260 through R2265. 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 display is produced on
the CRT during this time-slot.
Time-slot pulses 1, 2, and 3 are also connected to pin 4
of (J2260 through VR2262, VR2263, and VR2264 respec­
tively and R2262-R2265. 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 which is
displayed during time-slot 4 (1-2-5 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 by the plug-in. The Word
Trigger pulse connected to pin 8 of U2260 through C2255
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 as encoded
by the plug-in units. When row 7 is encoded in coincidence
with columns 3 through 7 (usually encoded during time-slot
1), a decimal point is placed at one of the five locations on
the CRT identified in row 7 of the Character Selection
Matrix (Fig. 3-24). This instruction refers to the decimal
point location in relation to the total number of characters
that can be displayed on the CRT (see Fig. 3-36). For
example, if column 3 and row 7 are encoded during
time-slot 1, the system is instructed to place a decimal
point in location No. 3. As shown in Fig. 3-36, this displays
a decimal point before the third character that can be
displayed on the CRT (first three time-slots produce a space
whether data is encoded or not; see previous paragraph).
The simultaneous application of row 7 data to the Y-input
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