NJU6538 View Datasheet(PDF) - Japan Radio Corporation

Part Name

Description

Manufacturer

NJU6538

1/8, 1/9, 1/10 Duty BITMAP LCD DRIVER with KEY SCAN

Japan Radio Corporation  

NJU6538

(5-7) Key More Input

Key scan signal output terminal S0 to S4 output “H” level in state of Key More Input. Although Key state

is detected without diodes to prevent unexpected key scan signal flow, non-pressed key data may

change pressed key data in triple or more key Input as shown in Fig. 1 and incorrect key data may be

output to external MPU. For prevention of miss-recognition by incorrect key data, diodes should be

inserted in front of K0 – K4 terminals as shown in Fig. 3 or control program of MPU should ignore the

combination of key data miss-recognition. For example, 4 keys and more ON data should be ignored.

S0

Pressed key

S1

Miss-recognized key

S2

In case of 3 keys operation in left

S3

picture, if S3 terminal outputs “H”

signal, this signal goes around on

S4

the dotted line and non-pressed key

is miss-recognized as pressed key.

K0

K1

K2

K3

K4

Fig. 1 Miss-recognized example by key more input

In modes of power save 1 (S0=0, S1=1 / Keys on only S5 line are valid) or power save 2 (S0=0, S1=1

/ Keys on only S4 and S5 lines are valid), pay attention about the followings. When Key More Input is

operated across the valid line and invalid, non-pressed key is miss-recognized as pressed key. However,

Key data on the invalid line is not read out and 4 keys and more operation in the mean time are not

ignored by MPU control program as shown in Fig. 2. In this case, diodes operate to prevent

miss-recognition as shown in Fig. 3.

S0

S0

S1

S1

No active key

S2

S2

S3

S3

S4

Active key

K0

S4

K1

K0

K2

Pressed key

K1

K3

K4

Miss-recognized key K2

K3

In case of power save 1, MPU control program can not

K4

decide ether correct key data or incorrect as shown

above because key data on only S4 line is read out to

MPU (all of key data on S3 line become to “0”.

Miss-recognition

prevent diodes

Fig. 2 Miss-recognition in power save 1

Fig. 3 Connect miss-recognition prevent diodes

- 18 -

Ver.2003-05-09

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