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B. 4 PUHC'l'IORS OF 'l'BB POD COR'fROLLBR
B.4.l Digital input register (3F7H Read)
Bit
7
6
5
4
3 I 2 I 1 1 0
DSCH
EXTB
EXTA
DSL
Not
used
+
DSCH (Disk Change)
When this bit (bit 7) is set to nln, it indicates that
the used disk may have been changed.
This bit is
effective only when internal 3.S-inch FDD is used, and
when the external FDD is used, this bit is always set
to "0".
+
EXTB (External FDD B)
When this bit (bit 6) is set to nl", the external FDD
Sel switch is set to Drive B.
+
EXTA (External FDD A)
When this bit (bit S) is set to nln, the external FDD
Sel switch is set to Drive B.
Ext. FDD Sel SW.
EFDSL 1
EFDAO
Status
1-2
0
1
Ext. FDD
Off
Off
1
1
Ext. FDD Drive B
2-3
1
0
Ext. FDD Drive A
B - 7
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