Key Scan Operation Functions

1.Key scan timing

The key scan period is 288T (s). To reliably determine the on/off state of the keys, this LSI scans the keys twice and

determines that a key has been pressed when the key data agrees. It outputs a key data read request (a low level on DO)

615T (s) after starting a key scan. If the key data does not agree and a key was pressed at that point, it scans the keys

again. Thus this LSI cannot detect a key press shorter than 615T (s).

2.Key scan operation

•The pins KS1 to KS6 are set to the high or low state by the control data.

•If a key on one of the lines corresponding to a KS1 to KS6 pin which is set high is pressed, the oscillator on the OSC

pin is started and a key scan is performed. Keys are scanned until all keys are released. Multiple key presses are

recognized by determining whether multiple key data bits are set.

•If a key is pressed for longer than 615T (s) (where T = 1/fosc) this LSI outputs a key data read request (a low level on

DO) to the controller. The controller acknowledges this request and reads the key data. However, if CE is high during a

serial data transfer, Do will be set high.

•After the controller reads the key data, the key data read request is cleared (DO is set high) and this LSI performs

another key scan. Also note that DO being an open-drain output, requires a pull-up resistor (between 1 k

Ω and 10 kΩ) .

No. 7632-10/16

LC75700T

Key on

*2. Not that the high/low states of these pins are determined by the control data, and that key scan output signals are not output

from pins that are set to low .

576T[s]

*2

1

1

2

2

3

3

4

4

5

5

6

6

KS4

KS5

KS6

KS3

KS2

*2

KS1

T=

1

fosc

*2

*2

*2

*2

*2

*2

*2

*2

*2

*2

Serial data transfer

Key data read request

Key data read

Key data read

Key data read

DO

DI

Key address (63H)

Key address

CE

Key scan

Key input 2

Key input 1

615T[s]

Key data read request

Key data read request

615T[s]

615T[s]

Serial data transfer

Serial data transfer

Key address

T=

1

fosc