Notes on the controller key data read techniques

1. Timer based key data acquisition

(1) Flowchart

(2) Timing chart

(3) Explanation

In this technique, the controller uses a timer to determine key on/off states and read the key data. The controller must

check the DO state when CE is low every t9 period without fail. If DO is low, the controller recognizes that a key has

been pressed and executes the key data read operation.

The period t9 in this technique must satisfy the following condition.

t9>t6+t7+t8

If a key data read operation is executed when DO is high, the read key data (KD1 to KD30) and sleep acknowledge

data (SA) will be invalid.

No. 6266-35/37

LC75804E, LC75804W

YES

NO

DO = [L]

CE = [L]

DO

DI

CE

Key on

Key on

t6

t9

t9

t9

t9

t5

t8

t8

t7

t7

t5

t7

t8

t5

t5: Key scan execution time when the key data agreed for two key scans. (615T(s))

t6: Key scan execution time when the key data did not agree for two key scans and the key scan was executed again. (1230T(s))

t7: Key address (43H) transfer time

t8: Key data read time

1

T = ———

fosc

Key data read

processing

Key input

Key scan

Key data read request

Key data read

Key address

Controller

determination

(Key on)

Controller

determination

(Key on)

Controller

determination

(Key off)

Controller

determination

(Key on)

Controller

determination

(Key off)