Serial Display; Decimal Point; Polarity And Unit Indication - Philips PM2517E Service Manual

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f n t h i s c i r c u i t t h e R C t i m e i s d e t e r m i n e d b v C 7 0 1 a n d R 7 2 1 . C 7 0 1 i s c o n n e c t e d t o + 8 . 5 V a n d R 7 2 1 i s
c o n n e c t e d t o s i g n a l D S 1 . ( D S 1 = 5 0 0 H z a n d s w i t c h i n g b e t w e e n 0 V a n d - 8 . 5 V ) . T h e r e s u l t i n g v o l t a g e o n
R 721 will be due to the resistor and capacitor about 4 V. The RC time. together with the switching point
o f t h e F E T V 7 0 5 w i l l r e s u l t i n a t i m e o f a b o u t 4 0 s e c . I n c a s e o f s T A N D B Y , l o g i c 0 ( - 8 . 5 V ) w i l l b e
c o n n e c t e d t o i n p u t B L o f t h e d i s p l a y u n i t v i a R 7 2 0 w h i c h m e a n s b l a n k e d d i s p l a y . W h e n p u s h b u t t o n
D ISPLAY is depressed, C 701 is discharged, FET V 705 starts conducting, causing transistor V 706 to conduct,
w h i c h g i v e s a l o g i c 1 r o t h e B L i n p u t w h i c h m e a n s t h a r t h e d i s p l a y i s n o t b l a n k e d . A f t e r 4 0 s e c . F E T V 7 0 5
switches again and the circuit is in its rest position again.
3.3.5.4. Serial displav (D51, DS2, DS = Digit Select)
S i g n a l s D S 1 a n d D 5 2 a r e s u p p l i e d t o t h e d u a l 1 o f 4 d e c o d e r D 7 0 2 { s e e t i m i n g d i a g r a m , F i g 2 5 )
T h e d e c o d e d s i g n a l s s w i t c h t h e r e l e v a n t L E D ' s i n t h e o r d e r 1 0 2 , 1 0 3 . t O 0 a n d 1 0 1 .
l n c a s e o f o v e r r a n g e ( i n d i c a t i o n > 9 9 9 9 = O O 0 O ) s i g n a l O V R i s t r u e ( l o g i c 1 ) a n d o n e p a r t o l t h e d u a l I o f 4
d e c o . i e r H E F 4 5 5 5 i s b l o c k e d ( N o e n a b l e ) . I n t h i s c a s e o n l y L E D 1 0 2 i s i g n i t e d a s t h i s o n e i s s w i t c h e d v i a
t h e o t h e r p a r t o f t h e H E F 4 5 5 5 ( e n a b l e )
3.3.5.6. Decimal point lDP3, DP2, DPI)
T h e d e c i m a l p o i n t i n f o r m a t i o n i s d i r e c t l y d e r i v e d f r o m t h e O O 0 0 5 5 l D 7 0 3 / 1 4 / 1 5 1 1 6 1 a n d i s s u p p l i e d t o t h e
c o r r e s p o n d i n g
d e c i m a l p o i n t s v i a a 2 7 0 Q r e s i s t o r ( s e e t a b l e a n d O O 0 0 5 5 s p e c i f i c a t i o n , c h a p t e r 3 . 3 . 5 3 . ) .
R a n q e
D P I D P 2 D P 3
9.999
9 9 . 9 9
999.9
1
0
0
0
1
0
0
0
1
3.3.5.7. Polaritv and unit indication
Unit indication
T h e u n i t i n d i c a t i o n i s m a d e w i t h t h e c o m b i n a t i o n o f L E D ' s a n d t h e p o s i t i o n o f t h e f u n c t i o n s e l e c t o r s w i t c h S 1
.
W h e n n o L E D i s l i g h t e d t h e p o s i t i o n o f t h e f u n c t i o n s e l e c t o r d e t e r m i n e s t h e u n i t i n d i c a t i o n e . g . f u n c t i o n k Q
a n d n o L E D i n d i c a t i o n ( O o r l V l Q )
m e a n s r a n g e k Q ( s e e t a b l e b e l o w ) .
Function
Signal OO 0055 Switches
L E D l i g h t e d lnd ication
m
v . \ , / v . . . ( 6 , 5 )
v . v / v . . . ( 6 , 5 )
ks2
I\,1, R NG C
R N G C
kst
K Q
kr)
rvfl
NUro
.... tlls2
.... a
kf2
+
- 6 0 . . . + 2 o o o c
( m ) A -
(m) A'v
Polarity indication (+ or -)
The polarity is indicated by means oi LED's.
T h e i n f o r m a t i o n f o r t h e L E D ' s i s d i r e c t l y d e r i v e d f r o m t h e O O 0 0 5 5 ( D 7 0 3 / 1 8 / 1 9 ) .
3.3.5.8. OVR (overrange)
I n c a s e o f o v e r r a n g e s i g n a l O V R b e c o m e s l o g i c 1 c a u s i n g d i g i t s 1 0 3 , 1 0 1 a n a 1 0 0 t o b e b l a n k e d '
O n l y d i g i t ' l 0 2 i s l i g h t e d .
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