Tektronix 7704A User Manual

Circuit Description -7704A
Service
The Character Generator stages p roduce the characters
which are displayed on the CRT
.
Any of the 50
characters
shown on the Character
Selection M atrix of F ig . 2-33 can
be ad d ressed
b y p roper selection of the column and row
currents . Only
one character is a d dressable in any one
time-slot ; α space can
b e a dd ed into the d isplayed wor d by
the Decimal
P
oint
L
ogic
and Character P osition Counter
stage
when encoded by the plug-in . The latter stage counts
the
number of characters generated an d produces an output
current to step the d isplay one character position to the
right for each c haracter . In a dd ition, the character p osition
is a d vanced once d uring each of time-slots 1, 2,
and 3,
whether α c haracter is generated during these
time-slots
or
not . This action fixes the starting
p
oint of
the stan d ar d -
format d isplay such t hat the first d igit of
the scaling factor
always starts at the same p oint within each word regar d less
of the information encoded in time-slot 1, 2, or 3 prece d
ing
this d igit . Also, by encoding row 10 and
column
0
during
any time-slot, α b lank s p ace can b
e
add
e
d
to the d isplay .
Decimal points can be added to
the d isplay at any time by
ad d ressing the appropriate
row and column (see Character
Selection M atrix for location of these
decimal points) . The
Decimal P oint L ogic and C haracter
P
osition
Counter stage
is reset after each word by the W ord
Trigger pulse .
The F ormat Generator stage provi d es the output signals
to the vertical an d h orizontal deflection systems of the
instrument to p ro d uce the character d isplay .
The
binary
Channel Address Code from
the Channel Counter stage is
connected to this stage, so that
the display from each
c hannel is p ositioned to
the
area of
the CRT associate d
with t he plug-in and
channel originating the word (see
F
ig .
2-32) . The p ositioning current or d ecimal p oint location
current generate d by the
Decimal P oint L ogic and
Character
P
osition
Counter stage is a dd e d to the H orizontal
( Χ 1 signal at
the input to the F ormat Generator stage to
provide
h
orizontal
p ositioning of the characters within each
wor d .
The Χ -
an
d Υ -Rea d out signals are connected to the
H orizontal
Amplifier and V ertical Amplifier through t
he
Χ -
and
Υ -Buffer stages .
The W ord Trigger stage pro d uces α trigger from the
E n d -of-Wor d p ulse generate d b y the Time-Slot Counter
stage after the tenth time-slot . This W or d Trigger pulse
advances the Channel Counter to d isplay the information
from the next channel or plug-in . It also p rovides α reset
p ulse to the Zeros L ogic and M emory stage and the Decimal
P oint L ogic and C haracter
P
osition Counter stage
. The
W ord Trigger stage can also b e a d
vanced
to j
ump α
complete word or α p ortion of α wor d when α
J ump
command is receive d from the
R
ow Data Switch stage
.
The Single-Shot L ockout stage allows the d is p lay
sequence
of
the R
ea
d out System to be change d . N ormally,
2- 44
t he
R
eadout
System operates in α free-running mode, so the
waveform d isplay is interrupte d randomly to d
isplay
characters . However, under certain conditions
(such
as
single-shot photogra p hy), it is d esirable that
the R eadout
System operate in α triggered
mode where the rea d out
p ortion of the d isplay
is normally b lanke d out, but can b e
p resented on comman
d . The Readout M ode input
from the
Output
Signals circuit d etermines the operating mo d
e of
the
R
ea dout
System .
Circuit Analysis of R eadout System
The following analysis of the Rea dout System discusses
the operation of each stage in d etail . Α complete schematic
of the R ea d out System is shown on diagram 10 at
the
rear
of this manual .
Timer
Timer U 3433 establishes
the timing se quence
for all
circuits within the R eadout System . This stage p roduces
seven time-related output waveforms (see F ig . 2-36) . The
triangle waveform p roduced at p in 6 forms the b asis for the
remaining signals . The basic perio d of this triangle wave-
form is about 250 microsecon d s as controlle d by RC
network
C3434-R3434 . The triangle waveform
is
clipped
an d
amplifie d by U 3433 to form the trapezoi d
al
output
signal at pin 10 .
The amplitu
d e of this out p ut
signal
is
exactly 15 volts as d
etermined
by U
3433
(exact
amplitu
d e
necessary to
accurately enco d e
d ata
in p lug-in
units ; see
E ncoding the Data) . The Trigger output
at
pin
5 p rovides
the switching signal for the Time-Slot Counter and Word
Trigger stages .
The signals at pins 12, 13, 14, an d 16 are pro d uced only
when the triangle waveform is on its negative slope and t he
trapezoidal waveform h as reached t he lower level . The
timing sequence of these waveforms is important to the
operation of the R ea d out System (see expande d waveforms
in F ig . 2-37) . The Ζ -Axis Inhibit at p in 14 is produced first .
This negative-going signal provi d es α b lanking pulse to the
CRT Circuit (see diagram 14) to blank t he
CRT
before the
display is switche d to the
R
eadout System
.
It also p
roduces
the Strobe pulse through Q3442 and CR3442 to signal
other stages within the
Rea
dout System to
begin
t
he
sequence necessary to pro d uce α c haracter . The collector
level of Q3442 is also connecte d to Character Generator
No . 2, U 3463, through C R3443 . This activates U 3463
d uring the quiescent perio d of the Strobe p
ulse
(collector
of Q3442 negative) and d
iverts the
outp
ut current of R ow
Decoder
U 3429 to
row 2 . The p ur p ose of this configuration
is to p revent
the Zeros L ogic and M emory stage U3401
from storing incorrect d ata d uring the q uiescent perio d of
the Strobe pulse . When the Strobe pulse goes positive,
CR3443 is reverse-biase d to d isconnect Q3442 from U 3463
and allow the R ow Decoder to operate in the normal
manner .
Ο

Tektronix 7704A Specifications

General

Brand	Tektronix
Model	7704A
Category	Test Equipment
Language	English