Tandy 1000 SL Technical Reference Manual page 306

2-2-2-2. F r o n t LED 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 of LED g a t e a n d LED d r i v e r .
They
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.
DRIVE SELECT
(E)
a n d I N USE (:)signals 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 LED g a t e . A c c o r d i n g t o t h e f u n c t i o n s e l e c t e d by U O / U l / I R 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 E
D s i g n a l t h r o u g h t h e
LED d r i v e r . W h i l e t h e
DLED
s i g n a l is L O W l e v e l , t h e f r o n t LED t u r n s o n .
Notes
1.
s:
O u t p u t s i g n a l f r o m r e a d y d e t e c t o r i n U 1 .
L O W i n r e a d y .
I U : I N USE i n p u t s i g n a l LOW.
IUL: I n t e r n a l s i g n a l of L S I .
L a t c h e d s i g n a l o f IN
USE by
l e a d i n g
edge o f
DRIVE SELECT.
2.
E
a n d IUL c o n d i t i o n s
a r e
e f f e c t i v e o n l y when t h e I U
s t r a p
i s
o n - s t a t e .
( T a b l e 204) F r o n t LED t u r n - o n c o n d i t i o n
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227
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