Tandy 1000 SL Technical Reference Manual page 307

2-2-2-3. Head load c o n t r o l c i r c u i t
The c i r c u i t s c o n s i s t s o f head load g a t e , o v e r d r i v e
t i m e r
1, s o l e n o i d
d r i v e r , and o v e r d r i v e c i r c u i t 1.
(1) Head l o a d g a t e
D R I V E SELECT and HEAD LOAD
(E:
s i g n a l s v i a s t r a p c i r c u i t a r e
i n p u t t o t h e head load g a t e i n t h e c o n t r o l LSI, U1. According t o t h e
s e l e c t e d f u n c t i o n d e s i g n a t e d by HL/HS s t r a p s , t h e s e i n p u t s i g n a l s a r e
g a t e d t o o u t p u t a s t h e HLC s i g n a l t o t h e s o l e n o i d d r i v e r U 3 ( p i n 3-14).
While t h e HLC s i g n a l
i s
H I G H l e v e l , t h e head load s o l e n o i d
i s
a c t i v a t e d .
Notes PRDY: Ready
f
Pre-ready
Pre-ready: I n t e r n a l s i g n a l o f LSI. I t goes t o TRUE 50msec
b e f o r e t h e ready s t a t e . Refer t o item 2-2-2-6.
(Table 205) Head load s o l e n o i d turn-on c o n d i t i o n
( 2 ) Solenoid d r i v e r
The H L C s i g n a l from t h e c o n t r o l LSI i s s u p p l i e d t o t h e d r i v e r I C , 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 o f U 3 .
( 3 ) Overdrive
t i m e r
1
The H L C s i g n a l i s 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
1 i n t h e c o n t r o l
LSI.
The o v e r d r i v e t i m e r i s 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 .
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