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58
ECR7700 Service Manual
Y111730 - 3
4-9 KEYBOARD CIRCUIT
Keyboard strobe line are the CPU port, this CPU port are P20-P22.
Keyboard Return lines are the CPU port, this CPU port are P60-63 and P64-67.
It is consist of matrix of Strobe line (8) × Return line (6).
This ports’ data is encoded by IC U4 of 74HC138 generated 8 stroke signals.
KSCN1
KSCN2
KSCN3
KSCN4
KSCN0
KSCN5
KSCN6
KSCN7
to KEY BOARD
C3
2
*100
pF
C3
3
*100
pF
C3
4
*100
pF
C3
5
*100
pF
C3
6
*100
pF
C3
7
*100
pF
C3
8
*100
pF
C3
9
*100
pF
R28
330 (Dip)
R29
330 (Dip)
R30
330 (Dip)
R31
330 (Dip)
R32
330 (Dip)
R33
330 (Dip)
1
2
3
4
5
6
7
8
9
CM2
*100pFx8
A
K
D4
1N4148
1
2
3
4
5
6
7
8
9
RM2
100k x 8
KR0
KR1
KR2
KR3
KR4
KR5
VCC
KRTN0
KRTN1
KRTN2
KRTN3
KRTN4
KRTN5
KRTN7
A
1
B
2
C
3
G1
6
G2A
4
G2B
5
Y0
15
Y1
14
Y2
13
Y3
12
Y4
11
Y5
10
Y6
9
Y7
7
VC
C
16
GN
D
8
U4
74HC138
VCC
VCC
C8
0.1uF
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
CN6
52147-1510
KSCN1
KSCN2
KSCN3
KSCN4
KSCN0
KSCN5
KSCN6
KSCN7
KR7
KS0
KS1
KS2
KR6
