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The SMI u s e s e x t e r n a l g a t e s i n t h e d e t e r m i n a t i o n of which PROM i s
enabled t o be r e a d .
4.3.5
Software
Refer t o F i g u r e 4 . 3 , F i g u r e 4 . 4 and 4 . 5 a s a n a i d i n t h e f o l l o w i n g
F i g u r e 4 . 3 i s a flow c h a r t which g i v e s t h e major s t e p s of t h e
d i s c u s s i o n .
program and t h e i r l o c a t i o n s i n memory.
When t h e i n s t r u m e n t i s t u r n e d
on,
t h e program i s r e s e t t o s t a r t from t h e b e g i n n i n g .
i n i t i a l i z e s i n t e r n a l r e g i s t e r s t o b e used i n t h e program.
m u l t i p l e x e d A/D i n f o r m a t i o n when t h e A/D c o n v e r t e r t e l l s i t t h e r e i s f r e s h
d a t a ready ( t h e program s t a y s i n a l o o p u n t i l t h e A/D s i g n a l s t h e r e i s i n -
f o r m a t i o n r e a d y ) .
S i n c e t h e A/D c y c l e s once e v e r y
.8
s e c o n d s , t h e program
t a k e s a l i t t l e under one second t o r u n t h r o u g h .
A t t h i s p o i n t , t h e program
The program i n p u t s
A f t e r t h e program h a s r e a d and s t o r e d t h e a p p r o p r i a t e s e n s o r v o l t a g e ,
i t
goes
t o t h e d a t a t a b l e of 3 2 b r e a k p o i n t v o l t a g e , t e m p e r a t u r e , and s l o p e
r e l a t i o n s h i p s .
The f i r s t b r e a k p o i n t ( s e e T a b l e 3 . 3 ) i s t h e l o w e s t v o l t a g e
and h i g h e s t t e m p e r a t u r e p o i n t w i t h t h e s l o p e b e i n g t h e s l o p e of t h e second
b r e a k p o i n t ( s i n c e t h e f i r s t b r e a k p o i n t does n o t h a v e a s l o p e t o a p o i n t
above i t ) .
The program f i n d s t h e c o r r e c t b r e a k p o i n t by checking each
b r e a k p o i n t v o l t a g e t o see i f i t i s lower t h a n t h e i n p u t v o l t a g e .
A s t h e
b r e a k p o i n t i s found, t h e t e m p e r a t u r e i s c a l c u l a t e d u s i n g t h e f o l l o w i n g
e q u a t i o n
:
T
=
(VBP -
VAD)
*
SBP + TBP
where
:
T
i s t e m p e r a t u r e i n
K
VBP
i s b r e a k p o i n t v o l t a g e
VAD
i s i n p u t v o l t a g e
SBP
TBP
i s b r e a k p o i n t t e m p e r a t u r e
dV
i s s l o p e between s u c c e s s i v e b r e a k p o i n t s (dT)
The t e m p e r a t u r e i s t h e n o u t p u t i n a s e r i a l form t o a s e r i a l - t o -
p a r a l l e l s h i f t r e g i s t e r which i s l a t c h e d i n t o a d e c o d e r d r i v e r t o f e e d t h e
d i g i t a l d i s p l a y b o a r d .
The l a t c h i n g of d a t a a v o i d s a f l i c k e r of t h e d i s p l a y
w h i l e t h e d a t a i s changing.
If
t h e i n s t r u m e n t i s a c o n t r o l l e r , t h e program c o n t i n u e s on t o
d e t e r m i n e t h e c o n t r o l f u n c t i o n ; i f n o t , i t l o o p s b a c k f o r t h e n e x t A/D
i n p u t .
To
p r e p a r e f o r c o n t r o l , t h e program i n i t i a t e s i n t e r n a l i n t e r r u p t
l e v e l s and v e c t o r s .
The s e t p o i n t can b e i n p u t i n one of two ways.
One
way i s t h e BCD s w i t c h e s
on
t h e f r o n t of t h e i n s t r u m e n t , t h e o t h e r i s through
t h e BCD
I/O
o p t i o n .
If
t h e f r o n t p a n e l s w i t c h e s a r e u s e d , t h e u s e r can d i a l
i n t h e c o n t r o l t e m p e r a t u r e d i r e c t l y i n K e l v i n d e g r e e s .
I f t h e e x t e r n a l BCD
o p t i o n i s u s e d , a BCD s i g n a l (from a s o u r c e s u c h as a computer) i s a p p l i e d
t o connector
J 1
( s e e T a b l e 3 . 2 ) .
In
o r d e r f o r t h e i n s t r u m e n t t o a c c e p t t h e
remote s e t p o i n t and d i s a b l e t h e BCD s w i t c h e s , a jumper on t h e c i r c u i t board
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