2. Interrupt based key data acquisition

• Flowchart

No. 5971-22/23

LC75893M

• Timing chart

• Explanation

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

must check the DO state when CE is low. If DO is low, the controller recognizes that a key has been pressed and

executes the key data read operation. After that the next key on/off determination is performed after the time t8 has

elapsed by checking the DO state when CE is low and reading the key data. The period t8 in this technique must

satisfy the following condition.

t8 > t4

If a key data read operation is executed when DO is high, the read key data (KD1 to KD20) and sleep acknowledge

data (SA) will be invalid.

t3·······Key scan execution time when the key data agreed for two key scans (420T[s]).

t4·······Key scan execution time when the key data did not agree for two key scans and the key scan was executed again (840T[s]).

t5·······Key address (43H) transfer time

t6·······Key data read time

1

T = ——

fosc

CE = [L]

DO = [L]

CE = [L]

DO = [H]