Tektronix 7704A User Manual

Circuit Description -7704A Service
T he Timer stage operates in one
of
two modes
as
co ntrolled b y th e Display-S kip level at p in 4 . T he b asic
mo d e j ust d escribed is α condition that d oes not occur
unless all ten characters of each wor d (80 characters total)
are d isplayed on the CRT . U
nder
typical conditions only α
few characters are d isplaye d
in
each wor d .
The
Display-Skip
level
at
p in 4 d etermines the p erio d of the Timer output
signal . When α character is to b e generate d , pin 4 is L O and
the circuit operates as j ust d escribe d . H owever, when α
character
is not to b
e
displaye d , α ΗΙ
level
is applied to p in
4 of U 3433 through C R3432 from the
Display-Skip
Generator stage . This signal causes the Timer
to
shorten its
perio d of o p eration to a b out 210 microsecon ds . T he
waveforms in Fig . 2-38 show the operation of the Timer
stage when the Display-Ski p con d ition occurs for all
p ositions in α wor d . N otice that there is no output at pins
12, 13, 14, an d 16 under this condition . This means that
the CRT d isplay is not interrupte d to d isplay characters .
Also notice that the triangle waveform at p in 6 d oes not go
as far negative, an d t hat th e negati v e portion of the
tra p ezoi d al waveform at p i n 10 is sh orter . Complete details
on op eration of the Display-Skip Generator are given later .
The Timer operation is also controlled by the Single-
Shot L ockout level at pin 2 . If this level is LO, the Timer
op erates as j ust d
escri
b
e
d .
H owever, if
t
h e Single-S h
ot
L ockout stage sets α
HI
level
at
this
p
in, the Timer stage is
locked
out
and
can
not produce
any output
signals
(see
Single-Shot L ockout d escription for further information)
READOUT intensity control R 5006 (see
diagram 11)
sets the i n tensity of the reado u t d isplay in d epen d ently
of
the Α or Β I N T EN SITY co n trols . T he RE ADO U T i n tensity
co n trol also p r ovi des α means of tu rning th e R
eadout
System off w hen α rea d out dis p lay is n ot d esire d . Wh en
R 5006 is turned fully counterclockwise, switch
S5006
opens . The current to pin 11 of U 3433 is interrupte
d , and
at the same time, α p ositive voltage is
applie d to p in 4
th roug h C R 3431 . T h e positive voltage switc hes the stage
to
the same con d itions as were p resent under t h e Display-S k i p
con d ition .
T
h erefore, the C R T display is not interru p te d to
p rese nt
c
h
aracters .
H
owever, time-slot p ulses continue to be
generated .
Time-Slot
Counter
Time-Slot Counter U 3445
is α sequential switch which
d irects the trapezoidal waveform input at pin
8 to
one
of its
10
output
lines
. These time-slot p ulses are used to
interrogate the
p lug-in units to obtain data for the R eadout
System . The
Trigger pulse at p in 15 switches the Time-Slot
Counter
to
the n
ext output line ; the output signal is
sequence
d
consecutively
from time-slot 1 through time-slot
10 . Figure 2-39 shows the time
relationship of the time-slot
pulses . N otice that
only
one line
carries α time-slot p ulse at
any given time . When time-slot
10 is completed, α negative-
2- 4 6
Fig .
2-38 . Timer stage operation w hen DisplaySkip condition
occurs .
f ιϋϋϋ
ον
Ι' ι
ϋ
ι ι
'
ι
'
ι
l
P i n 6
ι , J ϋ
il
k
i
Ι
ι
l
,
-
s
v
;
Ι
τοο ~ ι s
1
. 0v
ι ι
Pin 10
-
_~
τοο ;
Trigger
Pi n 5
Ι
,
1 1 ι 1 1 ~ ~~ _
ο ν
sv
ον
C haracter Scan
P in 16 ..
MEN
Ι
MMMM
ΙΙ
sv
Ζ -Axis ""
I nh i b it . .
P in 14
Ι ι Ι Ι i Ι Ι Ι Ι
IV 200,1 +
V - Η
Inhibit 1 1 ~
Ι
P in 13 ~~~ ρ V
Ζ
R eadout
Pin 12
~
+6 ν
Ι
ΝΟΤΕ : Test
. . . . . . . . .~ . . . . . . . . . . . . . . . .
oscilloscope externally
triggered from
. . . .
ΤΡ 3450 .

Tektronix 7704A Specifications

General

Brand	Tektronix
Model	7704A
Category	Test Equipment
Language	English