PD17012_15 Datasheet, PDF (244/320 Pages) Renesas Technology Corp – 4-BIT SINGLE-CHIP MICROCONTROLLERS WITH DIGITAL TUNING SYSTEM HARDWARE

µPD17012, 17P012
20.6 Using Key Source Controller/Decoder
20.6.1 Configuring key matrix
Figure 20-10 shows an example of configuring a key matrix.
As shown in this figure, the key matrix can be configured for up to 64 keys.
Because the key source signal output pins also output the LCD segment signals at the same time, diode A
must be used to prevent the reverse flow of the LCD segment signal if a momentary switch is used.
Diodes B and C are used to prevent sneaking of the key source signal.
Use a PNP transistor as the transistor switch.
The following (1) explains the points to be noted when an NPN transistor is used.
(2) through (4) explain the points to be noted if diodes A, B, and C are not used.
Figure 20-10. Example of Key Matrix Configuration
A
To LCD
B
panel
76 75 74 73
62 61 60 59
67 66 65 64 63 62 61 60 59 58
57 56 55 54 53 52 51 50 49 48
Configuration of each switch
52 50
43 42
(80 pin)
(64 pin)
Momentary switch
Alternate switch
Diode switch
KS
KS
KS
K
K
K
C
KS
KS
KS
K
K
K
Or
C
KS
K
242
Data Sheet U10101EJ4V0DS