Write/Erase C O N T R O L C I R C U I T - Tandy 1000 SL Technical Reference Manual

2-2-2-4. Write/erase c o n t r o l c i r c u i t
The c i r c u i t c o n s i s t s o f write/erase g a t e a n d erase t i m e r . Most o f t h e
p a r t s o f t h e c i r c u i t a r e e n c l o s e d i n t h e c o n t r o l LSI,
U1.
(1) Write/erase
g a t e
The g a t e j u d g e s w h e t h e r new d a t a c a n be w r i t t e n on a n i n s t a l l e d d i s k .
I f it c a n b e , t h e c i r c u i t s u p p l i e s t h e WG s i g n a l f o r t h e r e a d w r i t e
LSI a n d
erase t i m e r .
The WG s i g n a l
goes
t o TRUE i n t h e f o l l o w i n g c o n d i t i o n .
Notes
WG:
W r i t e o p e r a t i o n a t
H I G H .
-
DSEL: DRIVE SELECT i n p u t s i g n a l LOW.
IWG: WRITE GATE i n p u t s i g n a l LOW.
FPT: F i l e p r o t e c t s e n s o r o u t p u t (FPT i n p u t o f LSI) LOW.
-
The same a s t h a t t h e f i l e p r o t e c t s e n s o r d e t e c t s t h e w r i t e
e n a b l e n o t c h ( l i g h t p a s s i n g c o n d i t i o n ) o f
a
d i s k which
i s
e q u i v a l e n t t o t h a t t h e
E
(WRITE PROTECT) o u t p u t s i g n a l
1s
H I G H ( w r i t e - e n a b l e c o n d i t i o n ) .
( 2 ) E r a s e
timer
The c i r c u i t t o make t h e WG s i g n a l d e l a y from t h e
write/erase
g a t e
a s
i n
F i g . 2 0 5
t o
o u t p u t t h e EG s i g n a l f o r t h e r e a d
w r i t e
LSI. R e f e r t o i t e m
2-2-1-3.
V a r i o u s d e l a y
t i m e
c a n be
s e t
by HDS, HO, H 1 , a n d SS i n p u t t e r m i n a l s
Of t h e c o n t r o l LSI. By t h e s e i n p u t t e r m i n a l s , t h e o u t p u t o f HD a n d
SPED
t e r m i n a l s
are also s e t
which e x e c u t e s t h e s e l e c t i o n o f t h e FDD f u n c t i o n .
The s e t t i n g o f t h i s FDD, however,
i s
f i x e d
a s
shown i n t h e f o l l o w i n g
T a b l e .
-
231
-