1 2 .
VACUUM FLUORESCENT D I SPLAY BOARD
Theory
o f
Ope r a t i on
The vacuum f l uo r e s c e n t d i sp l a y ( VF D ) boa r d h a s a VFD and a 688 7 0 1 m i c r ocompu t e r .
The boa r d con t r o l s t he V F D by us i ng d a t a f r om t he MPU boa r d t h a t h a s been
processed t h r ough t he on-boa r d 6887 0 1 m i c r ocompu t e r .
Vacuum F l uo r e s c e n t D i sp l ay ( VF D )
T he VFD
i s a n e v acua t ed " t ube "
( g l a s s e n v e l ope )
con t a i n i ng
3 e l e c t r odes ;
c a t hode/ f i l amen t , g r i d , and anode .
No t e : E a c h c h a r a c t e r con t a i ns t he s e e l e c t rodes .
T h e c a t hode/ f l l amen t
i s a w i r e coa t e d w i t h a
m a t e r i a l wh i c h
f r ee l y em i t s
e l e c t rons when
an AC vo l t age i s app l i ed . A l so , t o e n s u r e t h a t t he
c h a r a c t e r
does not t u r n O N r an dom l y when n o t se l ec t e d , a c a t hode b i a s vo l t ag e ( E k ) mus t be
p r ov i de d .
T h i s I s done by s e t t i ng up a pos i t i ve DC vo l t a ge ( +5 VDC ) on wh i c h
t he
AC
f l l am e n t vo l t age r i de s .
When t he c h a r a c t e r i s not se l e c t e d ,
t h e
g r i d
vo l t age
I s t u r ne d O F F ( OVDC ) , wh i c h i s mo r e neg a t i ve
t h an t h e
AC
f i l amen t
vo l t age i mposed on t he + 5 V D C r e f e r ence vo l t age ( E k ) .
T h e g r i d e l e c t rode i s pos i t i oned b e t ween t h e c a t hode/ f i l amen t a n d t he
anode .
T h e g r i d s e r v e s a s a means t o a t t r a c t a n d acce l e r a t e f r ee e l e c t rons em i t t e d f r om
t he f i l ame n t o r I n h i b i t t h e e l ec t ron f l ow t owa r ds t he anode e l ec t rode .
T h e open
s c r een- I I ke
cons t r u c t i on of t he g r i d , e n a b l es i t to p a s s mos t of t he
e l e c t r ons
on t o t he a node .
The anode e l e c t rode s e r ve s a s t h e " r ece i ve r " o f t he f r ee e l e c t r ons .
i t i s
coa t e d w i t h a phosphor ma t e r i a l wh i c h em i t s a v i s i b l e I i g h t a f t e r b e i ng
s t r uck
by t he e l e c t rons , wh i c h a r e acce l e r a t e d by t he comb i ne d pos i t i ve vo l t ag e s of t he
g r i d and anode e l e c t r od e s .
I n t he case o f a dot t y pe d i s p l a y , t h i s anode
i s
segme n t e d i n t o 35 s e p a r a t e c i r cu l a r anode s .
T h e VFD r e qu i r e s a h i g h vo l t ag e t o i t s g r i d and anode e l emen t s for
p r oper
ope r a t i on .
VOL TAGE L EVEL
o
v.
F i g . 1 2- 1
STROBE 6
DOT MATRIX
DATA OUTPUT
+ 40VDC
F I L A M E NT
5.4VAC
PEAK to PEAK
1 2-3
Summary of Contents for 5000 Plus
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