Fdd Interface Circuitry - Tandy 1400LT Service Manual

FDD INTERFACE
Figure 4-25 shows the FDD interface circuitry.
Signal for FDD
:
"LOW" active DRIVE SELO-2 ( 3 . 5 ) , MOTOR ENA (3.5), "HIGH" active DRIVE SEL0,2 (5.25),
MOTOR ENA (5.25) are latched in the GATES. These are set by the I/O system command. The FDD control
signal for External 5.25 inch disk is driven by 74ALS240. The FDD control signal for the input system is pulled up
by the resistor. The External FDD (5.25) control signal and input signal for system are terminated by the capacitor.
]BOOT SELECT
s w
I
8 1 1 3
-
I N 1
9 9 9
EX1
D E F
r b
5.25FDD
6ATE5
74AL8240
I I I
I I I
r
I
IC57
J
17
75 100
*
FDC P O W D
A 0
li
N.C
-
0
% L 0 1 3 . m DRIV S a O / (3.6)
C
10
n
1
6
I
Figure 4-25. FDD Interface Circuitry
L
CNI z
. 2 7
. a
.
13
.
12
. 2 8
. Q
1
2
14
16
17
18
19
20
2 1
22
23
33
3 4
36
38
37
-
10
-
25
- 2 4
2 8
20
30
31
32
*
-N.C
-N.C
-N.C
-N.C
-N.C
-N.C
-U.C
-N.C
-N.C
-N.C
-N.C
-N.C
-N.C
-N.C
-N.C
-N.C
4-37