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Europaisches Patentamt
European Patent Office @ Publication number: 0 1 0 3 3 2 4 A 2
Office europeen des brevets
© EUROPEAN PATENT A P P L I C A T I O N
® Application number: 83201191.0 © Int. CI.3: H 04 M 11/06, H 04 Q 1 1 / 0 4
@ Date of filing : 1 5.08.83
@ Priority: 10.09.82 US 41 6441 @ Applicant: MOTOROLA, INC., 1303 East Algonquin Road, Schaumburg Illinois 60196 (US)
x*. r, * , u i- . . • n-inooj © Inventor: Wurzburg, Henry, 12506 Wistful Cove, Round ® Da f°fPuA^at,°nofaPPllcatlon:21-03-84 ^ Road Texas 78664 (US) Bulletin 84/12 1 '
@ Representative: Ibbotson, Harold, Motorola Inc Patent and Licensing Operations - Europe Viables Industrial
@ Designated Contracting States: DE FR GB IT NL Estate, Basingstoke Hants RG22 4PD (GB)
@ Simultaneous voice and data transmission circuit having a digital loop transceiver.
A digital PABX (10) having a plurality of digital line cards (22, 22') for coupling the PABX (10) to respective dig- ital subscriber sets (44) via subscriber lines is provided. In each digital line card (22), a digital loop transceiver (36) operates in a master mode and in each digital subscriber set (44), a digital loop transceiver (36') operates in a slave mode. The digital loop transceivers (36, 36') may also pro- vide simultaneous voice and data communication on a sin- gle channel, with a digital PCM voice word having a data bit embedded therein. Formatting and reformatting means are used to replace a predetermined PCM voice bit with a data bit to provide fast digital simultaneous communication on a single channel.
T e c h n i c a l F i e l d
T h i s i n v e n t i o n r e l a t e s g e n e r a l l y to t e l e c o m m u n i c a t i o n s
s y s t e m s a n d , more p a r t i c u l a r l y , to a v o i c e and d a t a
c i r c u i t in a d i g i t a l t e l e p h o n e s y s t e m c o m p r i s i n g a d i g i t a l
PABX and a p l u r a l i t y of d i g i t a l s u b s c r i b e r s e t s .
B a c k g r o u n d A r t
When a v o i c e c a l l is made u s i n g a c o n v e n t i o n a l a n a l o g
s u b s c r i b e r s e t , o n l y a s m a l l p o r t i o n of t he f r e q u e n c y
s p e c t r u m a v a i l a b l e on t h e t y p i c a l s u b s c r i b e r l i n e i s
u t i l i z e d . D u r i n g t h e d e v e l o p m e n t of d i s t r i b u t e d d a t a
p r o c e s s i n g s y s t e m s , an e f f o r t was made to u t i l i z e t h e
e x i s t i n g s u b s c r i b e r l i n e n e t w o r k to f a c i l i t a t e
c o m m u n i c a t i o n of t h e d i g i t a l d a t a u s e d by s u c h s y s t e m s .
V a r i o u s t y p e s of m o d u l a t o r / d e m o d u l a t o r (modem) d e v i c e s
h a v e b e e n d e v e l o p e d to t a k e a d v a n t a g e of t he l a t e n t
c a p a b i l i t y of t h e s u b s c r i b e r l i n e n e t w o r k to s u p p o r t
d i g i t a l d a t a c o m m u n i c a t i o n a t d a t a r a t e s s i g n i f i c a n t l y
g r e a t e r t h a n t h a t r e q u i r e d f o r a n a l o g v o i c e c o m m u n i c a t i o n .
For e x a m p l e , s y n c h r o n o u s modems a r e c o m m e r c i a l l y a v a i l a b l e
w h i c h u t i l i z e t h e d i f f e r e n t i a l p h a s e s h i f t k e y e d (DPSK)
m o d u l a t i o n / d e m o d u l a t i o n t e c h n i q u e to p r o v i d e d a t a
c o m m u n i c a t i o n a t r a t e s up to 9600 b a u d . H o w e v e r , e v e n i n
t he d i g i t a l p r i v a t e a u t o m a t i c b r a n c h e x c h a n g e s ( P A B X s )
w h i c h s u p p o r t i n t r a - e x c h a n g e c o m m u n i c a t i o n of v o i c e
i n f o r m a t i o n in t he fo rm of d i g i t a l PCM v o i c e d a t a w o r d s ,
t h e r e s p o n s e c h a r a c t e r i s t i c s of t h e s e v e r a l a n a l o g
c o m p o n e n t s of t he t y p i c a l a n a l o g ' l i n e c a r d u s e d t h e r e i n
g e n e r a l l y p r e v e n t r e l i a b l e c o m m u n i c a t i o n a t h i g h e r r a t e s .
S e v e r a l t e c h n i q u e s h a v e b e e n p r o p o s e d f o r p r o v i d i n g
h i g h e r s p e e d d i g i t a l d a t a c o m m u n i c a t i o n b e t w e e n
s u b s c r i b e r s t h r o u g h s u c h PABXs. H o w e v e r , s u c h p r o p o s a l s
t y p i c a l l y r e q u i r e t he i n s t a l l a t i o n of a d d i t i o n a l p a i r s o f
s u b s c r i b e r l i n e s to s u b s c r i b e r s r e q u i r i n g t h e s e r v i c e
a n d / o r r e d e s i g n / m o d i f i c a t i o n of t he p a r t i c u l a r PABX t o
p r o v i d e t h e c a p a b i l i t y to p r o c e s s t h e d i g i t a l d a t a w o r d s
in a m a n n e r d i f f e r e n t f rom the d i g i t a l PCM v o i c e d a t a
w o r d s . S i m u l t a n e o u s v o i c e and d a t a c o m m u n i c a t i o n a t h i g h
d i g i t a l s p e e d s has b e e n i m p l e m e n t e d w i t h d u a l c h a n n e l s a n d
f o u r - w i r e s y s t e m s . H o w e v e r , known s i n g l e c h a n n e l t w o - w i r e
s y s t e m s h a v i n g s i m u l t a n e o u s v o i c e and d a t a d i g i t a l
c o m m u n i c a t i o n r e q u i r e a d d i t i o n a l s w i t c h i n g s t r u c t u r e s a n d
an e x i s t i n g PABX c a n n o t be u s e d w i t h o u t s u b s t a n t i a l
m o d i f i c a t i o n .
SUMMARY OF THE INVENTION
A c c o r d i n g l y , i t i s an o b j e c t of t h e p r e s e n t i n v e n t i o n
to p r o v i d e an i m p r o v e d c o m m u n i c a t i o n s y s t e m .
A n o t h e r o b j e c t of t h e i n v e n t i o n is to p r o v i d e a
s i m u l t a n e o u s v o i c e and d a t a c i r c u i t f o r c o m m u n i c a t i o n
u s i n g a c o n v e n t i o n a l t w o - w i r e s u b s c r i b e r l i n e .
Yet a n o t h e r o b j e c t of t he i n v e n t i o n i s to p r o v i d e a
s i m u l t a n e o u s v o i c e and d a t a c i r c u i t u t i l i z i n g a d i g i t a l
l o o p t r a n s c e i v e r (DLT) and t w o - w i r e s u b s c r i b e r l i n e .
In c a r r y i n g o u t t h e a b o v e and o t h e r o b j e c t s of t h e
p r e s e n t i n v e n t i o n , t h e r e i s p r o v i d e d , in one f o r m , a c o m m u n i c a t i o n s y s t e m in w h i c h d i g i t a l d a t a is t r a n s f e r r e d
b e t w e e n a t e l e p h o n e s e t and a d i g i t a l l o o p t r a n s c e i v e r
(DLT) c i r c u i t h a v i n g a d i g i t a l I /O p o r t v i a a s u b s c r i b e r
l i n e . The DLT c i r c u i t c o m p r i s e s r e c e i v e r means f o r
r e c e i v i n g a f i r s t d i g i t a l d a t a word f rom t he d i g i t a l I / O
p o r t and w h i c h h a s a f i r s t s i g n a l l i n g b i t e m b e d d e d
t h e r e i n . M o d u l a t i o n means s e r i a l l y m o d u l a t e t he f i r s t
d i g i t a l d a t a word and t h e f i r s t s i g n a l l i n g b i t f o r
t r a n s m i s s i o n v i a t h e s u b s c r i b e r l i n e . Sync d e t e c t i o n
means d e t e c t a m o d u l a t e d s i g n a l on t h e s u b s c r i b e r l i n e a n d
p r o v i d e a v a l i d s y n c s i g n a l in r e s p o n s e to t he d e t e c t i o n .
D e m o d u l a t i o n means s e r i a l l y d e m o d u l a t e a s e c o n d d i g i t a l
d a t a word and a s e c o n d s i g n a l l i n g b i t r e c e i v e d v i a t h e
s u b s c r i b e r l i n e in r e s p o n s e to t h e v a l i d s y n c s i g n a l .
T r a n s m i t t e r means t r a n s m i t t he s e c o n d d i g i t a l d a t a w o r d
h a v i n g t h e s e c o n d s i g n a l l i n g b i t e m b e d d e d t h e r e i n to t h e
d i g i t a l I /O p o r t . T h u s , t h e DLT may s e l e c t i v e l y i n s e r t
and e x t r a c t a p r e d e t e r m i n e d b i t of a PCM v o i c e s i g n a l a n d
r e p l a c e t h e p r e d e t e r m i n e d b i t f o r use as a s e c o n d d a t a
p a t h .
The a b o v e and o t h e r o b j e c t s , f e a t u r e s and a d v a n t a g e s
of t h e p r e s e n t i n v e n t i o n w i l l be more c l e a r l y u n d e r s t o o d
f rom t h e f o l l o w i n g d e t a i l e d d e s c r i p t i o n t a k e n i n
c o n j u n c t i o n w i t h t he a c c o m p a n y i n g d r a w i n g s .
B r i e f D e s c r i p t i o n of t h e D r a w i n g s
FIG. 1 is a b l o c k r e p r e s e n t a t i o n of a p r i v a t e
a u t o m a t i c b r a n c h e x c h a n g e ( P A B X ) .
FIG. 2 is a s c h e m a t i c d i a g r a m of an a n a l o g l i n e c a r d
f o r use in t h e PABX of FIG. 1 .
FIG. 3 i s a d i g i t a l l i n e c a r d f o r use in t h e PABX o f
FIG. 1 .
FIG. 4 i s a d i g i t a l s u b s c r i b e r s e t to c o m m u n i c a t e
o v e r a s u b s c r i b e r l i n e w i t h t he d i g i t a l l i n e c a r d o f
FIG. 3 .
FIG. 5 i s a d i g i t a l l o o p t r a n s c e i v e r (DLT)
c o n s t r u c t e d in a c c o r d a n c e w i t h t he p r e s e n t i n v e n t i o n f o r
use in t h e d i g i t a l l i n e c a r d of FIG. 3 and t h e d i g i t a l s u b s c r i b e r s e t of FIG. 4 .
FIG. 6 i s a s c h e m a t i c r e p r e s e n t a t i o n of a f o u r - w i r e
c o m m u n i c a t i o n s y s t e m b e t w e e n t h e DLT in t he d i g i t a l l i n e
c a r d o f F IG . 3 and t h e DLT in t he d i g i t a l s u b s c r i b e r s e t
of FIG. 4 .
F IG. 7 i s a t i m i n g d i a g r a m i l l u s t r a t i n g a t y p i c a l
e x c h a n g e b e t w e e n t h e DLT in t he d i g i t a l l i n e c a r d o f
FIG. 3 and t h e PABX of FIG. 1 .
F IG . 8 is a t i m i n g d i a g r a m i l l u s t r a t i n g a t y p i c a l
e x c h a n g e b e t w e e n t h e DLT in t h e s u b s c r i b e r s e t of FIG. 4
and t h e c o d e c / f i l t e r t h e r e i n .
FIG. 9 i s a s c h e m a t i c r e p r e s e n t a t i o n of a t w o - w i r e
c o m m u n i c a t i o n s y s t e m b e t w e e n t h e DLT in t he d i g i t a l l i n e
c a r d of FIG. 3 and t h e DLT in t h e d i g i t a l s u b s c r i b e r s e t
o f FIG. 4 .
FIG. 10 i s a b l o c k r e p r e s e n t a t i o n of a s i m u l t a n e o u s
v o i c e and d a t a t r a n s m i s s i o n c i r c u i t c o n t s t r u c t e d i n
a c c o r d a n c e w i t h t h e p r e f e r r e d e m b o d i m e n t of t he p r e s e n t i n v e n t i o n .
D e s c r i p t i o n of t h e P r e f e r r e d E m b o d i m e n t
Shown in F IG. 1 i s a c o n v e n t i o n a l p r i v a t e a u t o m a t i c
b r a n c h e x c h a n g e (PABX) 10 c o m p r i s e d g e n e r a l l y of a m a i n
c a l l p r o c e s s o r 12 h a v i n g a s s o c i a t e d memory 14, a t i m e s l o t
i n t e r c h a n g e c i r c u i t 16, a s e t of c a l l p r o c e s s i n g
m i c r o p r o c e s s o r s 1 8 - 1 8 ' , e a c h h a v i n g an a s s o c i a t e d m e m o r y
2 0 - 2 0 ' , and a p l u r a l i t y of c o n v e n t i o n a l a n a l o g l i n e c a r d s
22. In t h e i l l u s t r a t e d f o r m , t h e PABX 10 a l s o i n c l u d e s a t
l e a s t two d i g i t a l l i n e c a r d s 22 ' c o n s t r u c t e d in a c c o r d a n c e
w i t h t h e p r e s e n t i n v e n t i o n .
In a t y p i c a l d i g i t a l t e l e p h o n e s w i t c h i n g s y s t e m s u c h
as t h e PABX 10, t h e m a i n c a l l p r o c e s s o r 12 c o o r d i n a t e s ,
v i a a s y s t e m bus 24 , t h e c a l l p r o c e s s i n g a c t i v i t i e s o f
e a c h of t h e s e v e r a l c a l l p r o c e s s i n g m i c r o p r o c e s s o r s
1 8 - 1 8 ' . In t u r n , e a c h of t h e c a l l p r o c e s s i n g
m i c r o p r o c e s s o r s 1 8 - 1 8 ' c o n t r o l s , v i a r e s p e c t i v e c o n t r o l
b u s e s 2 6 - 2 6 ' , t h e c o m m u n i c a t i o n of d i g i t a l PCM v o i c e d a t a
w o r d s v i a r e s p e c t i v e d a t a b u s e s 2 8 - 2 8 ' b e t w e e n t he s e v e r a l
l i n e c a r d s 22 a s s i g n e d to s u c h m i c r o p r o c e s s o r 1 8 - 1 8 ' .
In g e n e r a l , e a c h of t he a n a l o g l i n e c a r d s 22
c o m p r i s e s a t i m e s l o t a s s i g n m e n t and c o n t r o l c i r c u i t
(TSAC) 30 f o r s e l e c t i v e l y e n a b l i n g a c o d e c / f i l t e r 32 t o
d i g i t a l l y e n c o d e an a n a l o g v o i c e i n p u t s i g n a l r e c e i v e d v i a
a s u b s c r i b e r l i n e i n t e r f a c e c i r c u i t (SLIC) 34 f rom a
c o n v e n t i o n a l s i n g l e c h a n n e l s u b s c r i b e r s e t ( n o t s h o w n )
c o u p l e d to t i p and r i n g c o n d u c t o r s f o r o u t p u t as a d i g i t a l
p u l s e code m o d u l a t i o n (PCM) v o i c e d a t a word on t h e
r e s p e c t i v e d a t a bus 2 8 - 2 8 ' , and to d e c o d e a d i g i t a l PCM
v o i c e d a t a word r e c e i v e d on t h e d a t a bus 2 8 - 2 8 ' f o r o u t p u t
as an a n a l o g v o i c e o u t p u t s i g n a l to t he s u b s c r i b e r s e t
( n o t shown) v i a t h e SLIC 34. Shown in FIG. 2 i s a c i r c u i t
s c h e m a t i c f o r s u c h a c o n v e n t i o n a l a n a l o g l i n e c a r d 2 2 ,
u s i n g c o m p o n e n t s c o m m e r c i a l l y a v a i l a b l e f rom M o t o r o l a .
The v a r i o u s c o n t r o l and d a t a s i g n a l s w h i c h a r e p r o v i d e d t o
or by t h e l i n e c a r d 22 a r e g e n e r a l l y r e f e r r e d to as t h e
" b a c k p l a n e " of t he PABX 1 0 .
In a t y p i c a l t e l e p h o n e c a l l i n i t i a t e d by a s u b s c r i b e r
s e r v e d ' b y a " s o u r c e " l i n e c a r d 22 c o n t r o l l e d by , s a y , t h e
c a l l p r o c e s s i n g m i c r o p r o c e s s o r 18 to a s u b s c r i b e r s e r v e d
by a " d e s t i n a t i o n " l i n e c a r d 22 c o n t r o l l e d by , f o r
e x a m p l e , t h e c a l l p r o c e s s i n g m i c r o p r o c e s s o r 1 8 ' , t h e TSAC
30 on t h e s o u r c e l i n e c a r d 22 i n i t i a l l y d e t e c t s v i a t h e
a s s o c i a t e d SLIC 34 t h a t t h e s o u r c e s u b s c r i b e r s e t is o f f
h o o k , and r o u t e s t h e c a l l r o u t i n g i n f o r m a t i o n to t he c a l l
p r o c e s s i n g m i c r o p r o c e s s o r 18 f o r t r a n s f e r to t he m a i n c a l l
p r o c e s s o r 12. I f t he d e s t i n a t i o n l i n e c a r d 22 is n o t
i n d i c a t e d in t h e memory 14 as b e i n g b u s y , t he ma in c a l l
p r o c e s s o r 12 t h e n r e q u e s t s t he c a l l p r o c e s s i n g
m i c r o p r o c e s s o r 18' to n o t i f y t h e d e s t i n a t i o n l i n e c a r d 2 2
of t he c a l l . I f , upon p r o v i d i n g t h e s y s t e m - g e n e r a t e d r i n g
s i g n a l to t h e d e s t i n a t i o n s u b s c r i b e r s e t v i a t h e
r e s p e c t i v e SLIC 34, t h e a s s o c i a t e d TSAC 30 a d v i s e s t h e
c a l l p r o c e s s o r 18' t h a t t h e d e s t i n a t i o n s u b s c r i b e r s e t h a s
b e e n t a k e n o f f h o o k , t h e c a l l p r o c e s s i n g m i c r o p r o c e s s o r
18' a d v i s e s t h e m a i n c a l l p r o c e s s o r 12 t h a t t he r e q u e s t e d c o n n e c t i o n has b e e n e s t a b l i s h e d . D u r i n g a p a r t i c u l a r
t r a n s m i t t i m e s l o t a s s i g n e d by t he ma in c a l l p r o c e s s o r 1 2 ,
t h e TSAC 30 on t h e s o u r c e l i n e c a r d 22 e n a b l e s t h e
a s s o c i a t e d c o d e c / f i l t e r 32 to e n c o d e t he a n a l o g v o i c e
s i g n a l t h e n b e i n g r e c e i v e d f rom t h e s o u r c e s u b s c r i b e r s e t
v i a t h e SLIC 34 f o r o u t p u t as a d i g i t a l PCM v o i c e d a t a
word o n t o t h e d a t a bus 28. M e a n w h i l e , t h e main c a l l
p r o c e s s o r 12 has e n a b l e d the t i m e s l o t i n t e r c h a n g e c i r c u i t
16 to c o u p l e t h e d a t a bus 28 to t h e d a t a bus 28 ' t o
f a c i l i t a t e t he r e q u e s t e d i n t r a - e x c h a n g e c o m m u n i c a t i o n o f
t h e d i g i t a l PCM v o i c e d a t a w o r d . S i m u l t a n e o u s l y , t he TSAC
30 on t h e d e s t i n a t i o n l i n e c a r d 22 e n a b l e s t he a s s o c i a t e d
c o d e c / f i l t e r 32 to d e c o d e t h e d i g i t a l PCM v o i c e d a t a w o r d
on t h e d a t a bus 28 ' f o r o u t p u t as an a n a l o g v o i c e s i g n a l
to t h e d e s t i n a t i o n s u b s c r i b e r s e t v i a t he SLIC 34: In a
s i m i l a r m a n n e r , b u t d u r i n g a d i f f e r e n t r e c e i v e t i m e s l o t
a s s i g n e d by t h e m a i n c a l l p r o c e s s o r 12, t h e ' d e s t i n a t i o n
l i n e c a r d 22 i s a l l o w e d to e n c o d e t h e a n a l o g v o i c e s i g n a l
r e c e i v e d f r o m t h e d e s t i n a t i o n s u b s c r i b e r s e t f o r
t r a n s m i s s i o n as a d i g i t a l PCM v o i c e d a t a word v i a d a t a b u s
2 8 ' , i n t e r c h a n g e c i r c u i t 16 and d a t a bus 28 ' to t h e s o u r c e
l i n e c a r d 22 f o r d e c o d i n g and o u t p u t to t he s o u r c e
s u b s c r i b e r s e t . I f t h i s e x c h a n g e of d i g i t a l PCM v o i c e
d a t a w o r d s o c c u r s a t a s u f f i c i e n t l y h i g h f r a m e r a t e , s a y of t h e o r d e r of 8kHz , t h e n i t w i l l a p p e a r to e a c h of t h e
s u b s c r i b e r s t h a t t h e r e is a d i r e c t a n a l o g l i n k b e t w e e n
t h e i r r e s p e c t i v e s u b s c r i b e r s e t s .
In t h e g e n e r a l fo rm shown in FIG. 1, e a c h of t h e
d i g i t a l l i n e c a r d s 22 ' c o m p r i s e s a t i m e s l o t a s s i g n m e n t
and c o n t r o l c i r c u i t (TSAC) 30 ' f o r s e l e c t i v e l y e n a b l i n g a
d i g i t a l l o o p t r a n c e i v e r (DLT) 36 ( s e e FIG. 5) to r e c e i v e
d i g i t a l d a t a w o r d s v i a a s u b s c r i b e r l i n e i n t e r f a c e n e t w o r k
38 f rom a d u a l c h a n n e l , d i g i t a l s u b s c r i b e r s e t , such a s
t h a t shown in FIG. 4, w h i c h is c o u p l e d to r e s p e c t i v e
r e c e i v e and t r a n s m i t p a i r s of t i p and r i n g c o n d u c t o r s , f o r
d i r e c t o u t p u t on t h e r e s p e c t i v e d a t a bus 2 8 - 2 8 ' in t h e
same m a n n e r as t he d i g i t a l PCM v o i c e d a t a w o r d s a r e o u t p u t
by t h e c o d e c / f i l t e r 32 in t h e a n a l o g l i n e c a r d s 22; and t o
r e c e i v e d i g i t a l d a t a w o r d s on t he d a t a bus 2 8 - 2 8 ' f o r
d i r e c t o u t p u t to t h e s u b s c r i b e r s e t v i a t h e s u b s c r i b e r
l i n e i n t e r f a c e n e t w o r k 38. Shown in FIG. 3 is a c i r c u i t
s c h e m a t i c f o r t h e d i g i t a l l i n e c a r d 2 2 ' , w h e r e i n : t h e TSAC
30 ' c o m p r i s e s a p a i r of t he M o t o r o l a t i m e s l o t a s s i g n m e n t
c i r c u i t s ( T S A C s ) , one f o r e a c h of t he two d i g i t a l
c o m m u n i c a t i o n c h a n n e l s t he d i g i t a l l i n e c a r d 22 ' i s
c a p a b l e of s i m u l t a n e o u s l y s u p p o r t i n g ; t h e DLT 36 c o m p r i s e s
an i n t e g r a t e d c i r c u i t c o n s t r u c t e d in a c c o r d a n c e w i t h F I G .
5; and t h e s u b s c r i b e r l i n e i n t e r f a c e n e t w o r k 38 c o m p r i s e s
a t r a n s m i t i s o l a t i o n t r a n s f o r m e r 40 c o u p l e d to t h e t i p a n d
r i n g c o n d u c t o r s w h i c h c o m p r i s e t h e r e c e i v e p a i r of t h e
s u b s c r i b e r l i n e and a r e c e i v e i s o l a t i o n t r a n s f o r m e r 42 , c o u p l e d to t h e t i p and r i n g c o n d u c t o r s w h i c h c o m p r i s e t h e
t r a n s m i t p a i r of t he s u b s c r i b e r l i n e . As i l l u s t r a t e d i n
FIG. 3, t h e d i g i t a l l i n e c a r d 22 ' r e s p o n d s to and p r o v i d e s t h e same c o n t r o l and d a t a s i g n a l s w h i c h a r e p r o v i d e d to o r
by t h e a n a l o g l i n e c a r d 22 v i a t h e b a c k p l a n e of t h e PABX
1 0 .
Shown in FIG. 4 is a d u a l c h a n n e l , d i g i t a l s u b s c r i b e r
s e t 44. In g e n e r a l , t he s u b s c r i b e r s e t 44 c o m p r i s e s a
d i g i t a l l o o p t r a n s c e i v e r (DLT) 36 ' ( s e e FIG. 5) f o r
r e c e i v i n g d i g i t a l d a t a w o r d s f rom t he d i g i t a l l i n e c a r d
22' ( s e e FIG. 3) v i a a s u b s c r i b e r l i n e i n t e r f a c e n e t w o r k
38 ' c o u p l e d to r e s p e c t i v e r e c e i v e and t r a n s m i t p a i r s o f
t i p and r i n g c o n d u c t o r s , f o r o u t p u t , i f d i g i t a l PCM v o i c e
d a t a w o r d s , to a c o n v e n t i o n a l c o d e c / f i l t e r 32 ' f o r
s u b s e q u e n t d e c o d i n g and o u t p u t as an a n a l o g v o i c e o u t p u t v i a a v o i c e I /O n e t w o r k 46, o r , i f d i g i t a l d a t a w o r d s , t o
a s u b s c r i b e r d a t a p r o c e s s o r ( n o t shown) v i a a d a t a p o r t
48; and f o r t r a n s m i t t i n g d i g i t a l d a t a w o r d s p r o v i d e d
e i t h e r by t h e c o d e c / f i l t e r 32 ' in t he fo rm of d i g i t a l PCM
v o i c e d a t a w o r d s or by t h e s u b s c r i b e r d a t a p r o c e s s o r i n
t h e f o rm of d i g i t a l d a t a w o r d s , to t h e d i g i t a l l i n e c a r d
22' v i a t h e s u b s c r i b e r l i n e i n t e r f a c e n e t w o r k 3 8 ' . In t h e
p r e f e r r e d f o r m , t h e v o i c e I /O n e t w o r k 46 i n c l u d e s a v o i c e
i n p u t p o r t i o n 50, and a v o i c e o u t p u t p o r t i o n 52; t h e DLT
36 ' c o m p r i s e s an i n t e g r a t e d c i r c u i t c o n s t r u c t e d i n
a c c o r d a n c e w i t h FIG. 5; and t h e s u b s c r i b e r l i n e i n t e r f a c e
n e t w o r k 38 ' c o m p r i s e s a t r a n s m i t i s o l a t i o n t r a n s f o r m e r 4 0 '
c o u p l e d to t h e t i p and r i n g c o n d u c t o r s w h i c h c o m p r i s e t h e
t r a n s m i t p a i r of t h e s u b s c r i b e r l i n e and a r e c e i v e
i s o l a t i o n t r a n s f o r m e r 42 ' c o u p l e d to t he t i p and r i n g
c o n d u c t o r s w h i c h c o m p r i s e t he r e c e i v e p a i r of t h e
s u b s c r i b e r l i n e . In t h e i l l u s t r a t e d f o r m , a c o n v e n t i o n a l
t o n e g e n e r a t o r 54, s u c h as t h e M o s t e k MK5087, i n t e r a c t s
w i t h a d i a l k e y p a d 56 and t h e v o i c e I /O n e t w o r k 46 t o
p r o v i d e t h e c a l l r o u t i n g i n f o r m a t i o n r e q u i r e d to e s t a b l i s h ,
e a c h o f t h e two c o m m u n i c a t i o n c h a n n e l s , w h i l e a
c o n v e n t i o n a l hook s w i t c h 58 p r o v i d e s c a l l i n i t i a t i o n
s i g n a l l i n g i n f o r m a t i o n to t h e DLT 3 6 ' . An a u d i b l e
i n d i c a t i o n of an i n c o m i n g c a l l is p r o v i d e d v i a a r i n g i n g
t r a n s d u c e r 60. A s u b s c r i b e r s e t p o w e r s u p p l y 62 d e r i v e s
o p e r a t i n g p o w e r f o r t h e s e v e r a l c o m p o n e n t s of t h e
s u b s c r i b e r s e t 44 f r o m t h e s u b s c r i b e r l i n e in a
c o n v e n t i o n a l m a n n e r .
Shown in FIG. 5 i s a b l o c k d i a g r a m of t h e d i g i t a l
l o o p t r a n s c e i v e r (DLT) 36. In g e n e r a l , t h e DLT 36
c o m p r i s e s a d i g i t a l i n t e r f a c e p o r t i o n 64 f o r i n t e r f a c i n g
w i t h t h e PABX 10 in a m a s t e r o p e r a t i n g mode and w i t h t h e
c o d e c / f i l t e r 32 and s u b s c r i b e r d a t a p r o c e s s o r in a s l a v e
o p e r a t i n g mode , a m o d u l a t o r / d e m o d u l a t o r p o r t i o n 66 f o r
t r a n s m i t t i n g and r e c e i v i n g d i g i t a l d a t a w o r d s v i a t h e
s u b s c r i b e r l i n e , and a s e q u e n c e r and c o n t r o l p o r t i o n 68
f o r c o n t r o l l i n g t h e s e q u e n c e of o p e r a t i o n s p e r f o r m e d b y
t h e d i g i t a l i n t e r f a c e and m o d u l a t o r / d e m o d u l a t o r p o r t i o n s
64 and 66, r e s p e c t i v e l y .
In t h e d i g i t a l i n t e r f a c e p o r t i o n 64, a r e c e i v e (RX)
c o n t r o l c i r c u i t 70 r e s p o n d s to e i t h e r of two c h a n n e l
r e c e i v e e n a b l e s i g n a l s , RE1 and RE2, by e n a b l i n g a r e c e i v e
(RX) r e g i s t e r 72 of t h e s h i f t r e g i s t e r t y p e to s e r i a l l y
r e c e i v e d i g i t a l d a t a b i t s v i a a r e c e i v e (RX) t e r m i n a l i n
s y n c h r o n i z a t i o n w i t h a r e c e i v e d a t a c l o c k (RDC) on a
CLK/RDC t e r m i n a l . When a p r e d e t e r m i n e d " f r a m e " of d a t a
( s e e d i s c u s s i o n b e l o w ) has b e e n r e c e i v e d , t h e s e q u e n c e r and c o n t r o l p o r t i o n 68 e n a b l e s t he RX r e g i s t e r 72 t o
t r a n s f e r t he " t r a n s m i t " f r a m e of d a t a in p a r a l l e l i n t o a
t r a n s m i t t e r (XMIT) r e g i s t e r 74 in t h e m o d u l a t o r /
d e m o d u l a t o r p o r t i o n 66. S i m u l t a n e o u s l y , t he t h e n - c u r r e n t
s t a t e s of t h e two c h a n n e l s i g n a l l i n g b i t s on r e s p e c t i v e
S1I and S21 t e r m i n a l s a r e l a t c h e d and i n s e r t e d i n t o t h e
f r a m e of d a t a in t h e XMIT r e g i s t e r 74. S u b s t a n t i a l l y
i n d e p e n d e n t l y , t he s e q u e n c e r and c o n t r o l p o r t i o n 6 8
e n a b l e s a t r a n s m i t (TX) r e g i s t e r 76 to r e c e i v e a " r e c e i v e "
f r a m e of d a t a in p a r a l l e l f rom a r e c e i v e r (RCV) r e g i s t e r
78 in t h e m o d u l a t o r / d e m o d u l a t o r p o r t i o n 6 6 .
S i m u l t a n e o u s l y , t he two c h a n n e l s i g n a l l i n g b i t s in t h e
r e c e i v e f r a m e of d a t a a r e l a t c h e d and o u t p u t t e d o n
r e s p e c t i v e S10 and S20 t e r m i n a l s . In r e s p o n s e to e i t h e r
of two c h a n n e l t r a n s m i t e n a b l e s i g n a l s , TE1 and TE2, a
t r a n s m i t (TX) c o n t r o l c i r c u i t 80 e n a b l e s t h e TX r e g i s t e r
76 to s e r i a l l y t r a n s m i t t h e r e c e i v e f r a m e of d a t a v i a a TX
t e r m i n a l in s y n c h r o n i z a t i o n w i t h a t r a n s m i t d a t a c l o c k
(TDC) on an X1/TDC t e r m i n a l .
In t h e m o d u l a t o r / d e m o d u l a t o r p o r t i o n 66, a d i g i t a l t o
a n a l o g c o n v e r t e r (DAC) c o n t r o l c i r c u i t 82 p e r i o d i c a l l y
e n a b l e s a d i g i t a l to a n a l o g c o n v e r t e r (DAC) 84 to t r a n s m i t
t h e t r a n s m i t f r a m e of d a t a in t he XMIT r e g i s t e r 74 to t h e
t r a n s m i t t r a n s f o r m e r 40 in t h e s u b s c r i b e r l i n e i n t e r f a c e
n e t w o r k 38 u s i n g a d i f f e r e n t i a l p a i r of o u t p u t d r i v e r s 86
and 88 c o u p l e d to r e s p e c t i v e l i n e o u t p u t t e r m i n a l s L01 a n d
L02. In a p r e f e r r e d f o r m , t h e DAC 84 u t i l i z e s a b u r s t
d i f f e r e n t i a l p h a s e s h i f t k e y e d (DPSK) m o d u l a t i o n t e c h n i q u e
a t a c a r r i e r f r e q u e n c y of 256 kHz. S u b s t a n t i a l l y
i n d e p e n d e n t l y , an i n p u t b u f f e r 90 of t h e d i f f e r e n t i a l t o
s i n g l e e n d e d o u t p u t t y p e in t he m o d u l a t i o n / d e m o d u l a t i o n
p o r t i o n 66 c o u p l e s t h e s i g n a l r e c e i v e d f rom t h e r e c e i v e
t r a n s f o r m e r 42 in t h e s u b s c r i b e r l i n e i n t e r f a c e n e t w o r k 38
v i a l i n e i n p u t t e r m i n a l s LI1 and LI2 to a s y n c d e t e c t o r 9 2
v i a a w indow d e t e c t o r 94 and to a c o r r e l a t o r 96 v i a a
c o m p a r a t o r 98. As p h a s e s h i f t s of t h e p r o p e r fo rm a r e
d e c o d e d by t h e c o r r e l a t o r 96, t h e " d e c o d e d " b i t s a r e
s h i f t e d i n t o a s h i f t r e g i s t e r p o r t i o n t h e r e o f w h i c h
m a i n t a i n s t he mos t r e c e n t l y r e c e i v e d s e t o f
d a t a b i t s w h i c h m i g h t c o n s t i t u t e a f r a m e . When t he e n e r g y of a DPSK s i g n a l of t h e p r o p e r f r a m e l e n g t h is d e t e c t e d ,
t h e s y n c d e t e c t o r 92 p r o v i d e s a v a l i d s y n c s i g n a l t o
e n a b l e t h e c o r r e l a t o r 96 to t r a n s f e r t he r e c e i v e f r a m e o f
d a t a b i t s b e i n g m a i n t a i n e d t h e r e i n , in p a r a l l e l to t h e RCV
r e g i s t e r 78. A s w i t c h e d c a p a c i t o r b a n d g a p r e f e r e n c e 100
s i m i l a r to t h a t shown and d e s c r i b e d in c o p e n d i n g U . S .
P a t e n t No. 4 , 3 7 5 , 5 9 5 p r o v i d e s a p r e c i s i o n r e f e r e n c e
v o l t a g e to t h e DAC 84, t h e w indow d e t e c t o r 94 , and t h e
c o m p a r a t o r 98. P e r i o d i c a l l y , t he o f f s e t s of t h e i n p u t
b u f f e r 90, t h e w i n d o w d e t e c t o r 94, t h e c o m p a r a t o r 98 , a n d
t h e b a n d g a p r e f e r e n c e 100 a r e z e r o e d by an a u t o - z e r o
c i r c u i t 102 in a m a n n e r s i m i l a r to t h a t shown a n d
d e s c r i b e d in U .S . P a t e n t No. 4 , 3 5 5 , 2 8 5 .
In o p e r a t i o n , t h e DLT 36 p r o v i d e s d u p l e x
c o m m u n i c a t i o n of d i g i t a l d a t a w o r d s on a p a i r o f
i n d e p e n d e n t c h a n n e l s and a s i g n a l l i n g b i t a s s o c i a t e d w i t h
e a c h o f t he c h a n n e l s , b e t w e e n t h e d u p l e x s u b s c r i b e r l i n e
and a d i g i t a l d a t a p o r t . In a t y p i c a l l i n e t r a n s m i s s i o n
o p e r a t i o n , t h e RX r e g i s t e r 72 s u c c e s s i v e l y r e c e i v e s a
d i g i t a l d a t a word f o r e a c h of t h e c h a n n e l s i n
s y n c h r o n i z a t i o n w i t h t h e r e c e i v e d a t a c l o c k , w i t h t h e
d i g i t a l d a t a word f o r t he f i r s t of t he c h a n n e l s b e i n g
r e c e i v e d f rom t h e d i g i t a l I /O p o r t v i a t h e RX t e r m i n a l i n
r e s p o n s e to t h e f i r s t of t he c h a n n e l r e c e i v e e n a b l e
s i g n a l s , RE1, and t h e d i g i t a l d a t a word f o r t h e s e c o n d o f
t h e c h a n n e l s b e i n g r e c e i v e d f rom the d i g i t a l I /O p o r t v i a
t h e RX t e r m i n a l in r e s p o n s e to t h e s e c o n d of t he c h a n n e l
r e c e i v e e n a b l e s i g n a l s , RE2. A f t e r t he l a s t d a t a b i t o f
t h e f r a m e has b e e n c l o c k e d i n t o t h e RX r e g i s t e r 72, b o t h
d a t a w o r d s a r e t r a n s f e r r e d to t h e XMIT r e g i s t e r 74, a n d
t h e t h e n - c u r r e n t s t a t e s of t h e r e s p e c t i v e c h a n n e l
s i g n a l l i n g b i t s on t h e S1I and S2I t e r m i n a l s a d d e d t o
c o m p l e t e t h e f r a m e . As s o o n as t h e f r a m e has b e e n
a s s e m b l e d , t h e DAC c o n t r o l c i r c u i t 82 a c t u a t e s t h e DAC 84
to s e r i a l l y m o d u l a t e t he f i r s t and s e c o n d d i g i t a l d a t a
w o r d s and t he r e s p e c t i v e c h a n n e l s i g n a l l i n g b i t s in t h e
f r a m e , f o r t r a n s m i s s i o n v i a t h e t r a n s m i t t r a n s f o r m e r 40 t o
one of t he p a i r s of w i r e s in t he s u b s c r i b e r l i n e .
In a t y p i c a l l i n e r e c e p t i o n o p e r a t i o n , t h e s y n c d e t e c t o r 92 m o n i t o r s t he s i g n a l r e c e i v e d v i a t he r e c e i v e
t r a n s f o r m e r 42 on t h e o t h e r p a i r of w i r e s in t h e
s u b s c r i b e r l i n e , and p r o v i d e s a v a l i d s y n c s i g n a l i n
r e s p o n s e to d e t e c t i n g t h e e n e r g y of a DPSK m o d u l a t e d
s i g n a l of t h e p r o p e r f r a m e l e n g t h . M e a n w h i l e , t h e
c o r r e l a t o r 96 has b e e n s e r i a l l y d e m o d u l a t i n g t h e
s e q u e n t i a l l y r e c e i v e d b i t s w h i c h m i g h t c o n s t i t u t e a f r a m e
c o n t a i n i n g a d i g i t a l d a t a word f o r e a c h of t h e c h a n n e l s
and t he r e s p e c t i v e c h a n n e l s i g n a l l i n g b i t s . In r e s p o n s e to t h e v a l i d s y n c s i g n a l , i n d i c a t i n g t h a t a v a l i d f r a m e
has i n d e e d b e e n r e c e i v e d , t he c o r r e l a t o r 96 t r a n s f e r s t h e
f r a m e to t h e RCVR r e g i s t e r 78. At an a p p r o p r i a t e t i m e
d e p e n d i n g upon the mode of o p e r a t i o n , t h e f r a m e is t h e n
t r a n s f e r r e d f rom t h e RCVR r e g i s t e r 78 to t h e TX r e g i s t e r
76 and t h e r e s p e c t i v e c h a n n e l s i g n a l l i n g b i t s l a t c h e d f o r
o u t p u t on t h e S10 and S20 t e r m i n a l s . The TX r e g i s t e r 76
t h e n s e q u e n t i a l l y t r a n s m i t s t he d i g i t a l d a t a w o r d s i n
s y n c h r o n i z a t i o n w i t h t h e t r a n s m i t d a t a c l o c k , w i t h t h e
d i g i t a l d a t a word f o r t h e f i r s t c h a n n e l b e i n g t r a n s m i t t e d
to t h e d i g i t a l I /O p o r t v i a t h e TX t e r m i n a l in r e s p o n s e t o
t h e f i r s t of t h e c h a n n e l t r a n s m i t e n a b l e s i g n a l s , TE1, a n d
t h e d i g i t a l d a t a word f o r t h e s e c o n d c h a n n e l b e i n g
t r a n s m i t t e d to t h e d i g i t a l I /O p o r t v i a t h e TX t e r m i n a l i n
r e s p o n s e to t h e s e c o n d of t he c h a n n e l t r a n s m i t e n a b l e
s i g n a l s , T E 2 .
Shown in FIG. 6 i s a s c h e m a t i c r e p r e s e n t a t i o n of a
f o u r - w i r e or d u p l e x s u b s c r i b e r l i n e w h i c h has been c o u p l e d
a t t h e e x c h a n g e end t h e r e o f to t h e DLT 36 in t he d i g i t a l
l i n e c a r d 22 ' v i a t h e t r a n s m i t and r e c e i v e t r a n s f o r m e r s 40
and 42, r e s p e c t i v e l y , and a t t h e s u b s c r i b e r end t h e r e o f t o
t h e DLT 36 ' in t h e d i g i t a l s u b s c r i b e r s e t 44 v i a t h e
t r a n s m i t and r e c e i v e t r a n s f o r m e r s 40' and 4 2 ' ,
r e s p e c t i v e l y . In t h e d u a l - c h a n n e l fo rm of t he d u p l e x
s y s t e m , a f r a m e of d a t a c o m p r i s e s an e i g h t b i t d i g i t a l
d a t a word f o r t h e f i r s t c h a n n e l , an e i g h t b i t d i g i t a l d a t a
word f o r t h e s e c o n d c h a n n e l , and t h e s i g n a l l i n g b i t s f o r
t h e f i r s t and s e c o n d c h a n n e l s . P r e f e r a b l y , t he f r a m e a l s o
i n c l u d e s a p a r i t y b i t , e i t h e r e v e n or o d d , as d e s i r e d . A
s u i t a b l e f r a m e f o r m a t is i l l u s t r a t e d in FIG. 6 .
In t h e d i g i t a l l i n e c a r d 22 ' shown in FIG. 3, t h e DLT
36 i s p l a c e d in t h e m a s t e r mode of o p e r a t i o n by a l o g i c
h i g h s i g n a l on a m a s t e r / s l a v e (M/S) t e r m i n a l . In t h e
m a s t e r mode , t h e DLT 36 e m u l a t e s t h e c o d e c / f i l t e r 32 w i t h
r e s p e c t to t h e b a c k p l a n e by r e c e i v i n g / t r a n s m i t t i n g t h e
d i g i t a l d a t a w o r d s j u s t l i k e t he c o d e c / f i l t e r 32, and b y
r e s p o n d i n g to t h e v a r i o u s c o n t r o l s i g n a l s j u s t l i k e t h e
c o d e c / f i l t e r 32. In p a r t i c u l a r , t h e RX r e g i s t e r 72
s u c c e s s i v e l y r e c e i v e s a d i g i t a l ' d a t a word f o r e a c h of t h e
c h a n n e l s in s y n c h r o n i z a t i o n w i t h t he d a t a c l o c k p r o v i d e d
by t h e PABX 10 v i a t h e b a c k p l a n e , w i t h t he d a t a word f o r
t h e f i r s t c h a n n e l b e i n g r e c e i v e d f rom t h e b a c k p l a n e v i a
t h e RX t e r m i n a l in r e s p o n s e to t h e RE1 s i g n a l p r o v i d e d b y
a r e s p e c t i v e one of t h e TSACs 30 d u r i n g t h e r e c e i v e t i m e
s l o t a s s i g n e d to t h e f i r s t c h a n n e l , and t h e d a t a word f o r
t h e s e c o n d c h a n n e l b e i n g r e c e i v e d f rom t he b a c k p l a n e v i a
t h e RX t e r m i n a l in r e s p o n s e to t he RE2 s i g n a l p r o v i d e d b y
t he o t h e r TSAC 30 d u r i n g the r e c e i v e t i m e s l o t a s s i g n e d t o
t h e s e c o n d c h a n n e l . In r e s p o n s e to t h e n e x t m a s t e r s y n c
i n p u t (MSI) r e c e i v e d v i a an X2/MSI t e r m i n a l a f t e r t he l a s t
d a t a b i t of t h e f r a m e has b e e n c l o c k e d i n t o t he RX
r e g i s t e r 72, b o t h d i g i t a l d a t a w o r d s a r e t r a n s f e r r e d t o
t h e XMIT r e g i s t e r 74, and t h e t h e n - c u r r e n t s t a t e s of t h e
r e s p e c t i v e c h a n n e l s i g n a l l i n g b i t s p r o v i d e d v i a t h e S 1 1
and S2I t e r m i n a l s by t h e TSACs 30, r e s p e c t i v e l y , a d d e d t o
c o m p l e t e t he f r a m e . As soon as t he f r a m e has b e e n
a s s e m b l e d , t h e DAC c o n t r o l c i r c u i t 82 a c t u a t e s t he DAC 8 4
to s e r i a l l y m o d u l a t e t h e f i r s t a n d s e c o n d d i g i t a l d a t a
w o r d s and t h e r e s p e c t i v e c h a n n e l s i g n a l l i n g b i t s in t h e
f r a m e , f o r t r a n s m i s s i o n v i a t he t r a n s m i t t r a n s f o r m e r 40 t o
t h e r e c e i v e p a i r of w i r e s in t h e s u b s c r i b e r l i n e .
S i m u l t a n e o u s l y , t h e s y n c d e t e c t o r 92 m o n i t o r s t h e
s i g n a l r e c e i v e d v i a t h e r e c e i v e t r a n s f o r m e r 42 on t h e
t r a n s m i t p a i r of w i r e s in t he s u b s c r i b e r l i n e , a n d
p r o v i d e s t h e v a l i d s y n c s i g n a l in r e s p o n s e to d e t e c t i n g
t h e e n e r g y of a DPSK m o d u l a t e d s i g n a l of t he p r o p e r f r a m e
l e n g t h . M e a n w h i l e , t h e c o r r e l a t o r 96 has b e e n s e r i a l l y
d e m o d u l a t i n g t h e s e q u e n t i a l l y r e c e i v e d b i t s w h i c h m i g h t c o n s t i t u t e a f r a m e c o n t a i n i n g a d i g i t a l d a t a word f o r e a c h
of t he c h a n n e l s and t he r e s p e c t i v e c h a n n e l s i g n a l l i n g
b i t s . In r e s p o n s e to t h e v a l i d s y n c s i g n a l , i n d i c a t i n g
t h a t a v a l i d f r a m e has i n d e e d been r e c e i v e d , t h e
c o r r e l a t o r 96 t r a n s f e r s t h e f r a m e to t h e RCVR r e g i s t e r 7 8 .
In r e s p o n s e to t h e n e x t MSI, t h e f r a m e is t h e n t r a n s f e r r e d
f rom t h e RCVR r e g i s t e r 78 to t h e TX r e g i s t e r 76 and t h e
r e s p e c t i v e c h a n n e l s i g n a l l i n g b i t s l a t c h e d f o r o u t p u t o n
t h e S10 and S20 t e r m i n a l s . The TX r e g i s t e r 76 t h e n
s e q u e n t i a l l y t r a n s m i t s t he d i g i t a l d a t a w o r d s i n
s y n c h r o n i z a t i o n w i t h t h e t r a n s m i t d a t a c l o c k p r o v i d e d b y
t h e PABX 10 v i a t h e b a c k p l a n e , w i t h t h e d i g i t a l d a t a w o r d
f o r t h e f i r s t c h a n n e l b e i n g t r a n s m i t t e d to t he b a c k p l a n e
v i a t h e TX t e r m i n a l in r e s p o n s e to t h e TE1 s i g n a l p r o v i d e d
by t h e f i r s t one of t h e TSACs 30 d u r i n g the t r a n s m i t t i m e
s l o t a s s i g n e d to t h e f i r s t c h a n n e l , and t he d i g i t a l d a t a
word f o r t h e s e c o n d d a t a c h a n n e l b e i n g t r a n s m i t t e d to t h e
b a c k p l a n e v i a t h e TX t e r m i n a l in r e s p o n s e to t he TE2
s i g n a l p r o v i d e d by t h e o t h e r TSAC 30 d u r i n g the t r a n s m i t
t i m e s l o t a s s i g n e d to t h e s e c o n d c h a n n e l . A t y p i c a l
s e q u e n t i a l i n t e r a c t i o n of t h e DLT 36 w i t h t h e TSACs 3 0 ,
and w i t h t h e PABX 10 i s i l l u s t r a t e d by way of e x a m p l e i n
t h e t i m i n g d i a g r a m of FIG. 7 .
In t h e s u b s c r i b e r s e t 44 shown in FIG. 4, t h e DLT 3 6 '
i s p l a c e d in t he s l a v e mode of o p e r a t i o n by a l o g . i c low o n
t h e m a s t e r / s l a v e (M/S) t e r m i n a l . In t h e s l a v e mode , t h e
DLT 36 ' e m u l a t e s t h e f u n c t i o n s of t h e TSAC 30 and t h e
b a c k p l a n e w i t h r e s p e c t to t h e c o d e c / f i l t e r 3 2 ' b y
p r o v i d i n g t h e d i g i t a l PCM v o i c e d a t a w o r d s and c o n t r o l
s i g n a l s n e c e s s a r y f o r t h e c o d e c / f i l t e r 32 ' t o o p e r a t e , a n d
by r e c e i v i n g t h e d i g i t a l PCM v o i c e d a t a w o r d s p r o v i d e d b y
t h e c o d e c / f i l t e r 32 ' j u s t l i k e t h e b a c k p l a n e . In t h i s
mode , t h e s y n c d e t e c t o r 92 m o n i t o r s t he s i g n a l r e c e i v e d
v i a t h e r e c e i v e t r a n s f o r m e r 42 ' on t h e r e c e i v e p a i r o f
w i r e s in t h e s u b s c r i b e r l i n e , and p r o v i d e s t h e v a l i d s y n c
s i g n a l in r e s p o n s e to d e t e c t i n g t h e e n e r g y of a DPSK
m o d u l a t e d s i g n a l of t h e p r o p e r f r a m e l e n g t h . M e a n w h i l e ,
t h e c o r r e l a t o r 96 has b e e n s e r i a l l y d e m o d u l a t i n g t h e
s e q u e n t i a l l y r e c e i v e d b i t s w h i c h m i g h t c o n s t i t u t e a f r a m e
c o n t a i n i n g a d i g i t a l d a t a word f o r e a c h of t h e c h a n n e l s
and t h e r e s p e c t i v e c h a n n e l s i g n a l l i n g b i t s . In r e s p o n s e to t h e v a l i d s y n c s i g n a l , i n d i c a t i n g t h a t a v a l i d f r a m e
has i n d e e d b e e n r e c e i v e d , t he c o r r e l a t o r 96 t r a n s f e r s t h e
f r a m e to t he RCVR r e g i s t e r 78. The f r a m e is t h e n p r o m p t l y
t r a n s f e r r e d f rom t h e RCVR r e g i s t e r 78 to t h e TX r e g i s t e r
76 and t he r e s p e c t i v e c h a n n e l s i g n a l l i n g b i t s l a t c h e d f o r
o u t p u t on t h e S10 and S20 t e r m i n a l s . The TX r e g i s t e r 7 6
t h e n s e q u e n t i a l l y t r a n s m i t s t he d i g i t a l d a t a w o r d s i n
s y n c h r o n i z a t i o n w i t h a t r a n s m i t d a t a c l o c k g e n e r a t e d by a
p r e s c a l e r and o s c i l l a t o r 104 u s i n g a c r y s t a l c o u p l e d
b e t w e e n t h e X1/TDC and X2/MSI t e r m i n a l s , w i t h t h e d i g i t a l
d a t a word f o r t h e f i r s t c h a n n e l b e i n g t r a n s m i t t e d to t h e
c o d e c / f i l t e r 32 ' v i a t h e TX t e r m i n a l in s y n c h r o n i z a t i o n
w i t h a TE1 s i g n a l g e n e r a t e d by t h e TX c o n t r o l 80 r e l a t i v e
to t h e l a s t v a l i d s y n c s i g n a l , and t h e d i g i t a l d a t a w o r d
f o r t he s e c o n d d a t a c h a n n e l b e i n g t r a n s m i t t e d to t he d a t a
p o r t 48 v i a t h e TX t e r m i n a l in s y n c h r o n i z a t i o n w i t h a TE2
s i g n a l g e n e r a t e d by t h e TX c o n t r o l 80 r e l a t i v e to t he l a s t
v a l i d s y n c s i g n a l .
In r e s p o n s e to e a c h of t h e v a l i d s y n c s i g n a l s
p r o v i d e d by t he s y n c d e t e c t o r 92, t he RX r e g i s t e r 72
s u c c e s s i v e l y r e c e i v e s a d i g i t a l d a t a word f o r e a c h of t h e
c h a n n e l s in s y n c h r o n i z a t i o n w i t h a r e c e i v e d a t a c l o c k
g e n e r a t e d by t h e s e q u e n c e r and c o n t r o l 68 , w i t h t h e
d i g i t a l PCM v o i c e d a t a word f o r t h e f i r s t c h a n n e l b e i n g
r e c e i v e d f rom t h e c o d e c / f i l t e r 32 ' v i a t h e RX t e r m i n a l i n
s y n c h r o n i z a t i o n w i t h an RE1 s i g n a l g e n e r a t e d by t h e RX
c o n t r o l 70 r e l a t i v e to t h e l a s t v a l i d s y n c s i g n a l , and t h e
d i g i t a l d a t a word f o r t he s e c o n d c h a n n e l b e i n g r e c e i v e d
f rom t he d a t a p o r t 48 v i a t h e RX t e r m i n a l in r e s p o n s e t o
an RE2 s i g n a l g e n e r a t e d by t he RX c o n t r o l 70 r e l a t i v e t o
t h e l a s t v a l i d s y n c s i g n a l . In r e s p o n s e to t h e n e x t v a l i d
s y n c s i g n a l p r o v i d e d by t he s y n c d e t e c t o r 92, b o t h d i g i t a l
d a t a w o r d s a r e t r a n s f e r r e d to t h e XMIT r e g i s t e r 74 and t h e
t h e n - c u r r e n t s t a t e s of t he r e s p e c t i v e c h a n n e l s i g n a l l i n g
b i t s p r o v i d e d v i a t he S1I and S2I t e r m i n a l s by t h e h o o k
s w i t c h 58 a n d , i f a p p r o p r i a t e , t he s u b s c r i b e r d a t a
p r o c e s s o r , r e s p e c t i v e l y , a r e a d d e d to c o m p l e t e t he f r a m e .
As s o o n as t h e f r a m e has b e e n a s s e m b l e d , t h e DAC c o n t r o l
c i r c u i t 82 a c t u a t e s t h e DAC 84 to s e r i a l l y m o d u l a t e t h e
f i r s t and s e c o n d d i g i t a l d a t a w o r d s and the r e s p e c t i v e
c h a n n e l s i g n a l l i n g b i t s in t h e f r a m e , f o r t r a n s m i s s i o n v i a
t h e t r a n s m i t t r a n s f o r m e r 40 ' to t he t r a n s m i t p a i r of w i r e s
in t h e s u b s c r i b e r l i n e . A t y p i c a l s e q u e n t i a l i n t e r a c t i o n
of t h e DLT 36 ' w i t h t he c o d e c / f i l t e r 32 ' and t h e
s u b s c r i b e r d a t a p r o c e s s o r i s i l l u s t r a t e d by way of e x a m p l e in t h e t i m i n g d i a g r a m of FIG. 8 .
The p r i o r d e t a i l e d d e s c r i p t i o n has p e r t a i n e d to a
c o m m u n i c a t i o n s y s t e m o p e r a t i n g in a d u a l - c h a n n e l m o d e
h a v i n g two p a i r s of w i r e s in e a c h s u b s c r i b e r l i n e . A
c o n v e n t i o n a l PABX a r c h i t e c t u r e has a l s o been a s s u m e d to b e
u s e d w i t h t h e DLT d i s c l o s e d .
A l t h o u g h t h e DLT 36 is d e s i g n e d to o p e r a t e p r i m a r i l y
in t h e d u a l - c h a n n e l mode o v e r a d u p l e x s u b s c r i b e r l i n e ,
t h e DLT 36 may a l s o be o p e r a t e d in an e x c h a n g e w h i c h h a s
o n l y one p a i r of w i r e s in e a c h s u b s c r i b e r l i n e by a p p l y i n g
a l o g i c h i g h to a f o r m a t (FOR) t e r m i n a l t h e r e o f . In t h e
i l l u s t r a t e d fo rm of s u c h a t w o - w i r e s y s t e m s h o w n in F I G .
9, t h e h a l f d u p l e x s u b s c r i b e r l i n e is c o u p l e d at t h e
e x c h a n g e end t h e r e o f to t h e DLT 36 in t h e d i g i t a l l i n e
c a r d 22 ' v i a a t r a n s m i t / r e c e i v e i s o l a t i o n t r a n s f o r m e r 1 0 6 ,
and a t t h e s u b s c r i b e r end t h e r e o f to t h e DLT 36 ' in t h e
d i g i t a l s u b s c r i b e r s e t 44 v i a a t r a n s m i t / r e c e i v e i s o l a t i o n
t r a n s f o r m e r 1 0 6 ' . In t h e d u a l - c h a n n e l fo rm of t he h a l f
d u p l e x s y s t e m , a f r a m e of d a t a c o m p r i s e s an e i g h t b i t
d i g i t a l d a t a word f o r t h e f i r s t c h a n n e l , t h e s i g n a l l i n g
b i t f o r t h e f i r s t c h a n n e l , and a s e c o n d s i g n a l l i n g b i t f o r
use by t h e s u b s c r i b e r d a t a p r o c e s s o r as a d i g i t a l d a t a
b i t . P r e f e r a b l y , t h e f r a m e a l s o i n c l u d e s a p a r i t y b i t ,
e i t h e r e v e n or o d d , as d e s i r e d . A s u i t a b l e f r a m e f o r m a t
i s i l l u s t r a t e d in FIG. 9. S i n c e o n l y a s i n g l e d i g i t a l
d a t a b i t may be t r a n s f e r r e d in e a c h f r a m e , t he e f f e c t i v e
d a t a b i t t r a n s m i s s i o n r a t e is o n l y 8kHz r a t h e r t h a n t h e
64kHz of t he d u p l e x s y s t e m . H o w e v e r , t h i s r e d u c e d d a t a
r a t e may be a c c e p t a b l e in s i t u a t i o n s w h e r e t h e c o s t t o
i n s t a l l t h e s e c o n d p a i r of w i r e s in t he s u b s c r i b e r l i n e
o u t w e i g h s t h e b e n e f i t s of h i g h e r t r a n s m i s s i o n r a t e .
Shown in FIG. 10 is an e x t e n s i o n of t h e t w o - w i r e
s y s t e m of FIG. 9 c o n s t r u c t e d in a c c o r d a n c e w i t h a
p r e f e r r e d e m b o d i m e n t of t h e p r e s e n t i n v e n t i o n . FIG. 10
i l l u s t r a t e s a s i m u l t a n e o u s v o i c e and d a t a t r a n s m i s s i o n
c i r c u i t 106 c o m p r i s i n g f i r s t and s e c o n d t e l e p h o n e s e t
p o r t i o n s and f i r s t and s e c o n d l i n e c a r d p o r t i o n s . T h e
f i r s t t e l e p h o n e s e t c o m p r i s e s a t e l e p h o n e 108 c o u p l e d to a
c o d e c / f i l t e r c i r c u i t 110 w h i c h is c o u p l e d to a DLT 112. A
c o n t r o l l e r 114 has s i g n a l b i t i n p u t and o u t p u t t e r m i n a l s
c o u p l e d to DLT 112 and has a d a t a i n p u t and o u t p u t
t e r m i n a l . DLT 112 is c o u p l e d to t h e f i r s t l i n e c a r d
p o r t i o n v i a a t w o - w i r e s u b s c r i b e r l i n e 116. The f i r s t
l i n e c a r d p o r t i o n c o m p r i s e s a DLT 118 w h i c h is c o u p l e d t o
s u b s c r i b e r l i n e 116. A c o n t r o l l e r 120 has s i g n a l b i t
i n p u t and o u t p u t t e r m i n a l s c o u p l e d to DLT 118. C o n t r o l l e r
120 i s a l s o c o u p l e d to a s i g n a l b i t e n a b l e t e r m i n a l ( S I E )
of DLT '118. T r a n s m i t / r e c e i v e d a t a p a t h s form a PCM
c o m m u n i c a t i o n bus 122 b e t w e e n DLT 118 and a DLT 124 of t h e
s e c o n d l i n e c a r d p o r t i o n . A c o n t r o l l e r 126 has s i g n a l b i t
i n p u t and o u t p u t t e r m i n a l s c o u l e d to DLT 124 and i s a l s o
c o u p l e d to a s i g n a l b i t e n a b l e t e r m i n a l of ( S I E ) of DLT
124. A t w o - w i r e s u b s c r i b e r l i n e 128 c o u p l e s DLT 124 to a DLT 130 of t he s e c o n d t e l e p h o n e s e t p o r t i o n . A c o n t r o l l e r 131 has s i g n a l b i t i n p u t and o u t p u t t e r m i n a l s c o u p l e d t o
DLT 130 and has a d a t a i n p u t and o u t p u t t e r m i n a l . DLT 130
is c o u p l e d to a c o d e c / f i l t e r c i r c u i t 132 w h i c h i s c o u p l e d
to a t e l e p h o n e 1 3 4 .
In o p e r a t i o n , v o i c e and d a t a t r a n s m i s s i o n c i r c u i t 106
a l l o w s s i m u l t a n e o u s v o i c e and d a t a to be r o u t e d in t h e PCM
d a t a t i m e s l o t of a d i g i t a l PABX. DLTs 118 and 1 2 4
f u n c t i o n as m a s t e r s o v e r DLTs 112 and 130 w h i c h f u n c t i o n
as s l a v e s . DLTs 118 and 124 i n s e r t and e x t r a c t a
p r e d e t e r m i n e d b i t of a PCM t r a n s m i t / r e c e i v e d a t a word f o r
use as an 8 K b i t / s e c o n d u s e r d a t a c h a n n e l b e t w e e n
t e l e p h o n e s 108 and 134 by use of i n t e r n a l f o r m a t t i n g a n d
r e f o r m a t t i n g m e a n s . In t h e p r e f e r r e d f o r m , t h e
p r e d e t e r m i n e d b i t i s c h o s e n as t he l e a s t s i g n i f i c a n t b i t
(LSB) of t h e t r a n s m i t / r e c e i v e d a t a word a l t h o u g h o t h e r
b i t s may be c h o s e n . Use of t h e LSB a l l o w s d a t a to b e
r o u t e d b e t w e e n two c o n v e r s i n g p a r t i e s w i t h o u t h a v i n g t o
m o d i f y t h e c o n t r o l or r o u t i n g h a r d w a r e or t h e s o f t w a r e o f
t h e PABX. In t h i s e m b o d i m e n t , t h e LSB of t he PCM v o i c e
word i s b e i n g r e p l a c e d or ' s t o l e n ' . H o w e v e r , use of t h e
LSB d o e s n o t n o t i c e a b l y d e g r a d e the v o i c e q u a l i t y .
In c o n v e n t i o n a l t e l e p h o n e o p e r a t i o n , a PCM v o i c e w o r d
and two s i g n a l l i n g b i t s , say S1 and S2, a r e s e n t f r o m
t h e t e l e p h o n e s e t as a t e n b i t b u r s t o v e r t he s u b s c r i b e r
l i n e 116. When t h e PCM v o i c e word is r e c e i v e d by DLT 1 1 8 ,
t h e PCM word i s r o u t e d to t he a p p r o p r i a t e l i n e c a r d a n d
t h e a p p r o p r i a t e s i g n a l b i t s o u t p u t t e d f rom DLT 118 f o r
s i g n a l l i n g . C o n t r o l s i g n a l b i t s f rom t he s e c o n d l i n e c a r d
and an a s s o c i a t e d PCM v o i c e word a r e r e c e i v e d by DLT 118
and t r a n s m i t t e d to t h e f i r s t t e l e p h o n e s e t in a s i m i l a r
m a n n e r . DLT 112 a p p l i e s t he PCM v o i c e word f rom DLT 118
to c o d e c / f i l t e r c i r c u i t 110 and o u t p u t s t he s i g n a l b i t s t o
c o n t r o l l e r 1 1 4 .
T y p i c a l l y , o n l y one s i g n a l b i t , say S1, is r e q u i r e d
to be t r a n s m i t t e d b e t w e e n a t e l e p h o n e s e t and a l i n e c a r d
f o r c a l l p l a c e m e n t and c o n t r o l . Use of o n l y one s i g n a l
b i t f r e e s t h e s e c o n d s i g n a l b i t S2 f o r use as a d u p l e x 8
K b i t / s e c o n d u s e r d a t a p a t h . The s e c o n d s i g n a l b i t m a y
t e r m i n a t e or o r i g i n a t e on t h e l i n e c a r d b u t a s e p e r a t e
d a t a p a t h and s w i t c h i n g a r r a n g e m e n t b e t w e e n l i n e c a r d s
m u s t be p r o v i d e d to e s t a b l i s h a ' d a t a c o n n e c t i o n b e t w e e n
t e l e p h o n e s e t s . By f o r c i n g t h e s i g n a l b i t i n s e r t e n a b l e
(S IE) t e r m i n a l to a l o g i c h i g h l e v e l on DLTs 118 and 124
w h i c h a l r e a d y have a PCM d a t a p a t h c o n n e c t i o n made by t h e
PABX, an i n b o u n d S2 s i g n a l b i t f rom an o r i g i n a t i o n
t e l e p h o n e s e t is no t o n l y o u t p u t as S2 OUT o n
o r i g i n a t i o n DLT, bu t is a l s o i n s e r t e d i n t o t h e LSB of t h e
PCM word of t h e o r i g i n a t i o n DLT w h i c h is r o u t e d to t h e DLT
of t h e d e s t i n a t i o n l i n e c a r d . At the d e s t i n a t i o n l i n e
c a r d , t h e S2 s i g n a l b i t is s t r i p p e d f rom t he PCM word b y
t h e d e s t i n a t i o n DLT and s u b s t i t u t e d f o r S2 IN f o r
t r a n s m i s s i o n to t h e d e s t i n a t i o n t e l e p h o n e s e t . At t h e
d e s t i n a t i o n t e l e p h o n e s e t , t h e S2 OUT b i t is o u t p u t t e d
by t h e d e s t i n a t i o n DLT as t h e S2 OUT b i t . T h e r e f o r e ,
d a t a on t h e o r i g i n a t i n g t e l e p h o n e s e t ' s S2 IN t e r m i n a l
a p p e a r s a t t h e d e s t i n a t i o n t e l e p h o n e s e t ' s S2 OUT
t e r m i n a l and v i c e v e r s a . I t s h o u l d be n o t e d t h a t n o
a d d i t i o n a l d a t a p a t h or s w i t c h i n g a r r a n g e m e n t is r e q u i r e d
s i n c e t he d a t a has ' h i t c h h i k e d ' on t he e s t a b l i s h e d PCM
v o i c e p a t h c o n n e c t i o n . In t h i s m a n n e r , d u p l e x v o i c e
c o n v e r s a t i o n s and 8 - k b a u d / s e c o n d u s e r d a t a can b e
s i m u l t a n e o u s l y r o u t e d b e t w e e n t e l e p h o n e s w i t h o u t s p e c i a l
s w i t c h i n g p r o v i s i o n s . The r e m a i n i n g s i g n a l b i t i s
u n a f f e c t e d in t h i s mode and may s i g n a l hook s t a t u s to t h e
l i n e c a r d p l u s r i n g commands to t he t e l e p h o n e . I t s h o u l d
be f u r t h e r n o t e d t h a t t he i n v e n t i o n may be p r a c t i s e d b y
c o n n e c t i n g t he s i g n a l b i t i n s e r t e n a b l e t e r m i n a l of s l a v e
DLTs 112 and 130 to c o n t r o l l e r s 114 and 131, r e s p e c t i v e l y , and p e r f o r m i n g t h e s i g n a l b i t i n s e r t i o n and s t r i p p i n g a t
t h e s l a v e DLTs i n s t e a d of a t t h e m a s t e r D L T s .
W h i l e t h e i n v e n t i o n has b e e n d e s c r i b e d in t h e c o n t e x t
of a p r e f e r r e d e m b o d i m e n t , i t w i l l be a p p a r e n t to t h o s e
s k i l l e d in t h e a r t t h a t t h e p r e s e n t i n v e n t i o n may b e
m o d i f i e d in n u m e r o u s ways and may a s s u m e many e m b o d i m e n t s
o t h e r t h a n t h a t s p e c i f i c a l l y s e t o u t and d e s c r i b e d a b o v e .
A c c o r d i n g l y , i t i s i n t e n d e d by t h e a p p e n d e d c l a i m s t o
c o v e r a l l m o d i f i c a t i o n s of t h e i n v e n t i o n w h i c h f a l l w i t h i n
t h e t r u e s p i r i t and s c o p e of t h e i n v e n t i o n .
1. A d i g i t a l l o o p t r a n s c e i v e r c i r c u i t f o r p r o v i d i n g
c o m m u n i c a t i o n b e t w e e n a s u b s c r i b e r l i n e and a d i g i t a l I / O
p o r t , t h e t r a n s c e i v e r c i r c u i t c o m p r i s i n g :
r e c e i v e r means f o r r e c e i v i n g a f i r s t d i g i t a l d a t a w o r d
h a v i n g a f i r s t s i g n a l l i n g b i t e m b e d d e d t h e r e i n f r o m
s a i d d i g i t a l I /O p o r t ;
m o d u l a t i o n means f o r s e r i a l l y m o d u l a t i n g s a i d f i r s t
d i g i t a l d a t a word and the f i r s t s i g n a l l i n g b i t f o r
t r a n s m i s s i o n v i a s a i d s u b s c r i b e r l i n e ;
s y n c d e t e c t i o n means f o r d e t e c t i n g a m o d u l a t e d s i g n a l
on s a i d s u b s c r i b e r l i n e , and p r o v i d i n g a v a l i d s y n c
s i g n a l in r e s p o n s e to s a i d d e t e c t i o n ;
d e m o d u l a t i o n means f o r s e r i a l l y d e m o d u l a t i n g , i n
r e s p o n s e to s a i d v a l i d s y n c s i g n a l , a s e c o n d d i g i t a l
d a t a word and a s e c o n d s i g n a l l i n g b i t r e c e i v e d v i a
s a i d s u b s c r i b e r l i n e ; a n d
t r a n s m i t t e r means f o r t r a n s m i t t i n g s a i d s e c o n d d i g i t a l
d a t a word h a v i n g t h e s e c o n d s i g n a l l i n g b i t e m b e d d e d
t h e r e i n to s a i d d i g i t a l I /O p o r t .
2. The d i g i t a l l o o p t r a n s c e i v e r c i r c u i t of c l a i m 1
f u r t h e r c o m p r i s i n g :
f o r m a t t i n g means f o r e x t r a c t i n g t h e f i r s t s i g n a l l i n g
b i t f rom s a i d d a t a word and s u b s t i t u t i n g t h e r e f o r a
p r e d e t e r m i n e d d i g i t a l v a l u e .
3. The d i g i t a l l o o p t r a n s c e i v e r c i r c u i t of c l a i m 2
f u r t h e r c o m p r i s i n g :
r e f o r m a t t i n g means f o r s u b s t i t u t i n g t he s e c o n d
s i g n a l l i n g b i t f o r t h e l e a s t s i g n i f i c a n t b i t o f
t h e s e c o n d d i g i t a l d a t a w o r d .
4. The d i g i t a l l o o p t r a n s c e i v e r c i r c u i t of c l a i m 1 w h e r e i n
s a i d s y n c d e t e c t i o n means a r e c h a r a c t e r i z e d as b e i n g
i n o p e r a t i v e when t he m o d u l a t i o n means a r e m o d u l a t i n g
s a i d f i r s t d i g i t a l d a t a word and t h e f i r s t s i g n a l l i n g
b i t .
5. The d i g i t a l l o o p t r a n s c e i v e r c i r c u i t of c l a i m 1 w h e r e i n
t h e f i r s t e m b e d d e d s i g n a l l i n g b i t is t he l e a s t
s i g n i f i c a n t b i t of t h e f i r s t d i g i t a l d a t a w o r d , and t h e
s e c o n d e m b e d d e d s i g n a l l i n g b i t is t he l e a s t s i g n i f i c a n t
b i t of t h e s e c o n d d i g i t a l d a t a w o r d .
6. The d i g i t a l l o o p t r a n s c e i v e r c i r c u i t of c l a i m 1 w h e r e i n
a t h i r d and a f o u r t h s i g n a l l i n g b i t i s a s s o c i a t e d w i t h
t h e f i r s t d i g i t a l d a t a w o r d , s a i d t h i r d s i g n a l l i n g b i t
b e i n g r e c e i v e d by t h e r e c e i v e r means in s y n c h r o n i z a t i o n
w i t h a f r a m e c l o c k and s a i d f o u r t h s i g n a l l i n g b i t b e i n g
t r a n s m i t t e d by t h e t r a n s m i t t e r means in s y n c h r o n i z a t i o n
w i t h a f r a m e c l o c k .
7. A d i g i t a l l o o p t r a n s c e i v e r c i r c u i t f o r p r o v i d i n g c o m m u n i c a t i o n b e t w e e n a s u b s c r i b e r l i n e and a d i g i t a l
I /O p o r t , t he t r a n s c e i v e r c i r c u i t c o m p r i s i n g :
r e c e i v e r means f o r r e c e i v i n g a f i r s t d i g i t a l d a t a w o r d
and a f i r s t s i g n a l l i n g b i t f rom s a i d d i g i t a l I / O
p o r t ;
m o d u l a t i o n means f o r s e r i a l l y m o d u l a t i n g s a i d f i r s t
d i g i t a l d a t a word w i t h t h e f i r s t s i g n a l l i n g b i t
e m b e d d e d t h e r e i n f o r t r a n s m i s s i o n v i a s a i d
s u b s c r i b e r l i n e ;
s y n c d e t e c t i o n means f o r d e t e c t i n g a m o d u l a t e d s i g n a l
on s a i d s u b s c r i b e r l i n e , and p r o v i d i n g a v a l i d s y n c
s i g n a l in r e s p o n s e to s a i d d e t e c t i o n ;
d e m o d u l a t i o n means f o r s e r i a l l y d e m o d u l a t i n g , i n
r e s p o n s e to s a i d v a l i d s y n c s i g n a l , a s e c o n d d i g i t a l
d a t a word h a v i n g a s e c o n d s i g n a l l i n g b i t e m b e d d e d
t h e r e i n and r e c e i v e d v i a s a i d s u b s c r i b e r l i n e ; a n d
t r a n s m i t t e r means f o r t r a n s m i t t i n g s a i d s e c o n d d i g i t a l
d a t a word and t h e s e c o n d s i g n a l l i n g b i t to s a i d
d i g i t a l I /O p o r t .
8. The d i g i t a l l o o p t r a n s c e i v e r c i r c u i t of c l a i m 7 f u r t h e r
c o m p r i s i n g :
f o r m a t t i n g means f o r e x t r a c t i n g t h e f i r s t s i g n a l l i n g
b i t f rom s a i d d a t a word and s u b s t i t u t i n g t h e r e f o r
a p r e d e t e r m i n e d d i g i t a l v a l u e .
9. The d i g i t a l l o o p t r a n s c e i v e r c i r c u i t of c l a i m 8 f u r t h e r
c o m p r i s i n g :
r e f o r m a t t i n g means f o r s u b s t i t u t i n g t h e s e c o n d
s i g n a l l i n g b i t f o r t he l e a s t s i g n i f i c a n t b i t o f
t h e s e c o n d d i g i t a l d a t a w o r d .
10. The d i g i t a l l o o p t r a n s c e i v e r c i r c u i t of c l a i m 7
w h e r e i n t h e s y n c d e t e c t i o n means a r e c h a r a c t e r i z e d a s
b e i n g i n o p e r a t i v e when t h e m o d u l a t i o n means a r e
m o d u l a t i n g s a i d f i r s t d i g i t a l d a t a word w i t h t he f i r s t
s i g n a l l i n g b i t .
