C Hannel Counter; Ockout - Tektronix 7904A Instruction Manual

T
heory of Operation-7904A
Slot Cou nter LO. This resets t h e Time-Slot Counte r to SI NGLE-S HOT
L
OC KOUT
time-slot 1 and holds it t h ere until the Word Tr igger is
The Single-Shot
L oc k o u t stage allows α single
r
eadou t
reset . At the same time, α HI level is applied to
p
in 4 of
frame (8 comp lete words) to be
d
isplayed on the crt,
th e Timer
t
h roug h
C
R2157 an d CR2125. Th is HI level
after wh ic h
t
he R ead out System is loc ked out, so f u rt her
causes t h e Timer to o perate i n
t
h e Disp lay-Sk i p mo de,
rea d out displays are not
p
rese nte d until t he circ u it is
so α
c
haracter is not generated .
reset . Integrated
c
i rcuit
U
2120C and
U
2120B are
co n nected to for m α b istab le fli p-flo p .
F
or free-run
T
he
n
ext Trigger
p ulse is not recognized by the Time-
operation, pin 8 of
U
2120C is
h
e ld HI . Th is activates
Slot Co u nter, si nce 02159 is loc k ed in time-slot 1 b
y
U
2120C an d results in α
L O output level at pin 10,
02155 .
H
owever, th is Trigger pu lse resets the
W
ord
enabling t h e Timer stage to op erate i n α free-ru n n i ng
Trigger stage th rough C2155 . Pin 13 of
U
2155D goes
L
O
ma nner.
t o e n a b le the Ti me-Slot Counter and Time r stages for
t h e
n
ext time-slot
p
u lse. Sim u ltaneously, when
U
2155D
The ou tp u t of th e Si n gle-S h ot
L
oc k o u t stage remai ns
switc hes out put states, the res u lting
n
egative-going
L
O to allow
U
2126 to operate i n the free-ru nn i n g mo d e
ed ge is connecte d to pi n 3 of
U
2155A . Th is res u lts in α
until α
L
O is received at pin 8 of
U
2120C. Whe n
t
h is
negative-going Word Trigger output at pi n 4 of
U
2155B
occurs, th e output level at pin 10 of
U
2120C
d
oes not
to ad vance t h e C h a nn el Co u nter to th e next word . When
change immed iately .
H
owever, the Si ngle Shot
L
oc k out
th e
n ext Trigger pulse is received at pin 15 of
U
2159 t h e
ci r cuit is now ena b led .
Time-Slot Cou n ter retu rns to the n ormal sequence of
o peration and produ ces an o utput on t h e time-slot 1
If t he Ch an nel Counter
h
as
n ot com p leted word 8, th e
li n e .
Read out System conti n ues to o perate in t h e normal
C
HANNEL CO UN TER
m an ner . Whe n word 8 is com p leted , the
n
egative-goi ng
e nd-of-frame pu lse is
p
ro duced at
p
i n 11 of
U
2250 as
Ch annel Cou nter
U
2250 is α bi nary cou n ter th at
the Chan n el Cou nte r
s h ifts to t h e code necessary to
p
rod uces the Ch annel Add ress Cod e for t h e Column
d
isplay word one. Th is
p ulse is app lie d to pi n 3 of
and Row Decoder stages an d
t
he
F
ormat Ge n erator
U
2120A w h ich
p
rod uces α Η # at pin 6 of
U
2120B
stage. This code instr u cts these stages to sequentially
b
ecause of t he momentary
L
O at
p
i n 2 . T h e HI at
p
in 6
select and dis play t h e 8 c h a n nels of d ata from the p
lug-
prod uces α
L
O at
p
in 4 which cau ses
p i n 9 of
U
2120C to
ins . Ta ble 3-12 g i ves t h e 8 comb i n ations of th e C h an nel go
L
O.
B
ecause
p in 8 is already
L
O,
p
in 10 goes HI . This
Add ress Code and the resu ltan t chan nel selected with
disab les t he Timer stage, so it o perates in th e Dis p lay-
each combination .
ski p mo de .
3-30
TABLE 3-12
Th e Si n gle-Shot
L oc k ou t stage remai n s in t h is cond itio n
C h annel Add ress Code
until α
p ositive-going trigger
p
ulse is app lied to
p
i n 8 of
S
N Β031766 &
B
elow
U
2120C . This trigger p u lse
p
rod uces α
L O at pi n 10 of
Pin 11
P
in 8
Pin 9 C h annel
U
2120C to enable
U
2126 an d
d
isable
U
2120B . Now, th e
02250
02250 02250 Displayed
Timer stage can operate in t h e
n
ormal man ner for
an other com p lete frame . When word 8 is complete d, th e
LO
L
O
L
O
Chan nel 2
C h a n n el Cou nter
p
rod uces another end-of-frame
p
ulse
Left Ve rtical to again lock out th e Timer stage.
LO
L
O
Hl
I
Channel l
L eft Vertical
EN CODI NG THE DATA
Η 1 LO Channel 2
Data is co n veyed from the
p
lug-i n un its to the Readout
L
O
R
ig h t Vertical
System in th e form of an analog (cu rrent level) code.
The c h aracters that can be se l ecte d by t h e encoded d ata
L
O
Η !
HI
Channel l
are s h own on the Ch aracter Selection
M
atrix (see
F ig . 3-
R ig ht Vertical
9) .
E
ac h
c
haracter req uires two cu rre nts to defi ne it;
these currents are i dentified as the colu mn current a nd
Η !
L
O
L
O
Channel 2 t
h e row current, corres pond ing to th e col u mn and row
Α
H
orizontal of th e matrix . The colum n and row
d
ata is encod ed by
p
rogra mming the
p lug-in un its .
F
igure 3-15 s hows α
HI
L
O
HI
Channel l
typical encoding sc heme u si ng resisto r s for α voltage-
Α
H
ori zontal
sensing amplifier
p
l u g-i n unit .
N
otice th at the 10 TS
HI
HI
L
O Channel 2
(time slot) pu lses prod uced by t he Time-Slot Co u nter
Β
H
orizontal
stage are con nected to the plug-in unit .
H
owever, time-
slots 5, 6, a n d 10 are n ot used by t he
p
lug-i n
u n it to
Η 1 HI
HI
Channel l
en code
d ata when
u
si n g t h e Standard Read out
F
ormat .
Β Horizontal
(See Tab le 3-11 for Sta nd ard Read out
F
ormat .) The
amplitud e of t h e ti me-slot
p
ulse is exactly -15 volts as
REV N OV 1985