lc75857e Sanyo Semiconductor Corporation, lc75857e Datasheet - Page 37

• Manufacturer Part Number: lc75857e
• Description: 1/3, 1/4 Duty Lcd Display Drivers With Key Input Function
• Manufacturer: Sanyo Semiconductor Corporation

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.
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.
Key input
Key scan
t9>t6+t7+t8
CE
DI
DO
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
Key data read
processing
DO = [L]
CE = [L]
YES
t5
determination
Controller
(Key on)
Key data read request
t7
NO
Key on
Key address
t8
Key data read
t9
t6
determination
Controller
(Key on)
T =——— = ——
LC75857E, LC75857W
t7
fosc
t8
1
t9
f
CK
1
determination
Controller
(Key off)
t5
t9
Key on
determination
Controller
(Key on)
t7
t8
t5
t9
determination
Controller
(Key off)
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