Dual 1-0F4 Decoder/Demultiplixer - Philips PM2517E Service Manual

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3-4-2. HEF 4555 B Dual 1-0f4 decoder/demultiplixer
HEF 4555 a 'l to 4 decoder-demultiplexer is used to decode the digit select outputs Ds1 and DS2 from
oo 0059.
I n c a s e o f o v e r l o a d s i g n a l o v L b e c o m e s l o g i c I a n d f o r c e s t h e o u t p u t s 4 , 6 a n d 7 o f t h e H E F 4 5 5 5 B t o l o w .
w h i c h m e a n s t h a t t h e d i g i t s ' l O o , 1 0 1 a n d 1 0 3 a r e b l a n k e d .
V s s ( - 8 . 5 V )
0 3
0 2
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v s s ( - 8 5 V )
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H E F 1 5 5 5
Fis.30.
T h e H E F 4 5 5 5 B i s a d u a l 1 o f 4 d e c o d e r / d e m u l t i p l e x e r .
E a c h h a s t w o a d d r e s s i n p u t s ( A g a n d A 1 ) , a n
a c t i v e L O W e n a b l e i n p u t { E T . a n d f o u r m u t u a l l y e x c l u s i v e o u t p u t s w h i c h a r e a c t i v e H I G H ( O 0 t o 0 3 ) .
When used as a decoder,Ewhen-H lG H, forces Og to 03 LOW. When used as a demultiplexer. the appropriate
output is selected by the data on A6 and A1. All unselected outputs are LOW.
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P I N N I N G
A q a n d 4 1
Og to 03
enable inputs (active LOW)
address inputs
o u t p u t s ( a c t i v e H I G H )
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A o A t
O g O 1 o.>
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