Tandy 1000 SL Technical Reference Manual page 317

Not-ready s t a t e
( E
o u t p u t
H I G H )
and t h e
S!EP
(E)
p u l s e i n p u t from
t h e h o s t c o n t r o l l e r i s ignored.
( 3 ) S h i f t r e g i s t e r and phase d r i v e s e l e c t o r
S t e p p u l s e and t h e o u t p u t of t h e d i r e c t i o n l a t c h a r e s u p p l i e d t o t h e
s h i f t r e g i s t e r and t h e phase d r i v e s e l e c t o r t o be converted t o t h e
a p p r o p r i a t e timing s i g n a l s f o r u n i - p o l a r 1-phase d r i v e o f t h e 4-phase
s t e p p i n g motor. These phase d r i v e s i g n a l s a r e o u t p u t from t h e c o n t r o l
LSI and s u p p l i e d t o t h e c o i l d r i v e r .
I n o r d e r t o improve t h e t o r q u e margin i n t h e seek o p e r a t i o n , p a r t i a l
2-phase d r i v e p e r i o d i s provided by t h e phase d r i v e s e l e c t o r only i n
t h e i n i t i a l s t a g e when t h e d r i v e phase is changed.
Refer t o Fig.211
f o r timing c h a r t .
( 4 )
Motor d r i v e r
Four o u t p u t s ,
PA, PB, PNA
and PNB
f r o m
t h e c o n t r o l LSI, U1 a r e i n p u t t o
t h e motor d r i v e r IC, U 3 . Refer t o Fig.208 a s t o t h e c o n s t r u c t i o n of U3.
(5) Overdrive timer
2
E x t e r n a l and i n t e r n a l s t e p p u l s e s a r e a l s o s u p p l i e d t o t h e o v e r d r i v e
t i m e r 2 i n t h e LSI. The o v e r d r i v e
t i m e r
2
is
c o n s t r u c t e d with a
r e t r i g g e r a b l e c o u n t e r .
During o n - s t a t e o f t h e t i m e r (24msec, a p p r o x . ) ,
S O D o u t p u t from t h e LSI goes t o
H I G H
l e v e l . Refer t o Fig.212.
-
238
-