Control Logic; D I S P L A Y; A D - Philips PM2517E Service Manual

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3.3.4.
Digital section
3.3.4.1. General
T h e d i g i t a l s e c t i o n c o n s i s t s o f t h e d i g i t a l c o n t r o l l C O O O O 5 g , t h e d i s p l a y c o n t r o l l C O O 0 0 5 5 a n d t h e
d i s p l a y .
A s c o n t r o l s i g n a l s f o r t h e d i g i t a l s e c t i o n a r e u s e d : ( F i g 2 2 ) '
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DATA
U P / D O W N / O
D H ( d a t a h o l d )
A U T
F A , F B , F C , F D
: f r o m t h e A D C . d e t e r m i n i n g t h e t i m r n g
: f r o m t h e A D C , d e t e r m i n i n g t h e d i s p l a y e d v a l u e
: d e t e r m i n i n g t h e r a n g e s i n c a s e o f m a n u a l r a n g l n g
: from the probe input
: d e t e r m i n i n g a u t o r a n g i n g
: function in{ormation from the Junction selector
A s o u t p u t s i g n a l s f o r t h e d i g i t a l s e c t i o n a r e u s e d : ( F i g 2 2 . )
R N G A , 8 , C
O V R
D S 1 . D S 2 , L A E N
A O , 4 1 , 4 2 , A 3
P O L
: r a n g e i n l o r m a t i o n i n t h e d i f f e r e n t f u n c t i o n s
: a u t o z e r o s i g n a l d e t e r m i n i n g t h e A Z p e r i o d o f t h e A D C
: o v e r r a n g e f o r t h e d i s p l a y t o q a v e o v e r l o a d
: d i g i t s s e l e c t / l a t c h e n a b l e
u s e d I o r s e r i a l a n d p a r a l l e d i s p l a y t i m i n g
: d a t a i n f o r m a t i o n , d e t e r m i n e d b Y
s i g n a l s F A , F B , F C , F D a n d R N G A , B , C
: u n i t i n d i c a c t i o n , d e t e r m i n e d b Y
s i q n a l s F A , F B , F C , F D a n d R N G A , B , C , a n d P O L
: P o l a r i t V o f t h e O O 0 0 5 9
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Fis. 2.
F o r d e t a i l e d i n f o r m a t i o n o f t h e s i g n a l s a l s o r e f e r t o t h e s p e c i f i c a t i o n s o f t h e l C ' s c o n c e r n i n g ( c h a p t e r 3 . 4 . )
3.3.4.2- Control logic (Fig.23)
The control logic, comprising the OO 0059 is the central processor of the Pl\,4 2517. ln the flow chart abridged
i n f o r m a t i o n i s g i v e n a b o u t t h e t i m i n g i n t h e O O 0 0 5 9 .
W h e n t h e i n s t r u m e n t i s s w i t c h e d o n t h e m e a s u r e m e n t s
a r e s t a r t e d . A f t e r t h e w a i t i n g t i m e s { o r i n p u t s e t t l l n g
a n d t i m i n g s e t t l i n g , t h e c o u n t e r s t a r t s c o u n t i n g t h e r e s u l t o f t h e A D C d u r i n g t h e f i r s t m e a s u r i n g p e r i o d . T h e
f i r s t m e a s u r i n g p e r i o d i s 1 2 2 8 8 c l o c k p u l s e s w h i c h a r e c o u n t e d b y t h e t i m e r .
The carry signal ol the timer changes the state of the control logic. At the same time the input voltage of the
A D C a r e s w i t c h e d w i t h t h e A Z s i g n a l s ( r e f e r t o 3 . 3 . 3 A D C ) .
After the waittime which is also used for input settling, the result is counted again in the second measuring
p e r i o d w h i c h i s a l s o 1 2 2 8 8 c l o c k p u l s e s . A f t e r t h e 2 n d m e a s u r i n g p e r i o d t h e r e s u l t o f t h e c o u n t e r i s d i s p l a V e d
The maximum contents of the counter is 2O.OOO- lf the counter result during one measurement is ) 10-000,
s i g n a l O V R ( o v e r r a n g e ) w i l l b e c o m e a c t i v e . D e p e n d e n t t o t h e i n s t r u m e n t s e t t i n g s ( N r l A N o r A U T ) , o v e r r a n g e
or auto ranging will be performed when the measurement is completed.
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