Mode S E L E C T O R - Tandy 1000 SL Technical Reference Manual

2-2-1-1. Mode s e l e c t o r
Mode s e l e c t o r i s c o n s t r u c t e d with t h e switch f i l t e r and w r i t e c u r r e n t
switch.
Table 201 shows t h e s w i t c h i n g c o n d i t i o n of t h e read w r i t e c i r c u i t
by
t h e t r a c k switch s i g n a l
( 5
and
SF1
s i g n a l s i n t h e schematic diagram)
from t h e c o n t r o l c i r c u i t .
(1) Switch f i l t e r
Switch f i l t e r i s used f o r e l i m i n a t i n g t h e i n f l u e n c e o f s a d d l e waveform
( r e f e r t o Fig.204) a t t h e o u t e r t r a c k s .
When t h e
5
and
SF1
a r e
C14 and
C1S
a r e a c t i v a t e d t o i n c r e a s e t h e c a p a c i t y o f t h e low p a s s
f i l t e r c a p a c i t o r , C16. T h i s s t a t e i s t h e o n - s t a t e of t h e switch f i l t e r ,
and t h e c u t - o f f frequency o f t h e low p a s s f i l t e r i s s e t t o low.
l e v e l , t h e switch f i l t e r c a p a c i t o r s ,
( 2 ) Write c u r r e n t switch
W r i t e c u r r e n t s w i t c h is used only f o r 9 6 t p i models.
I t
is used f o r
making t h e write c u r r e n t i n o u t e r t r a c k s h i g h e r than i n i n n e r t r a c k s
t o improve t h e o v e r - w r i t e c h a r a c t e r i s t i c s ( w r i t e 2F a f t e r 1F w r i t e
and measure t h e r e s i d u a l frequency components of 1 F ) .
W r i t e
c u r r e n t i s s u p p l i e d t o t h e w r i t e d r i v e r by w r i t e c u r r e n t source
i n t h e r e a d w r i t e LSI, U2. The s u p p l i e d value from t h i s c u r r e n t source
can
be
c a l c u l a t e d from t h e following e x p r e s s i o n combining t h e e x t e r n a l
r e s i s t o r s R6 and R7.
Outer t r a c k s : I w =
1 3 . 2
+
1 2 . 7
---
No.1
R6 R7
I n n e r t r a s k s : I w =
13.2
---
R 6 No.2
-
209
-