LC75886PW Datasheet, PDF (30/36 Pages) ON Semiconductor – 1/4 and 1/3-Duty LCD Display Driver

LC75886PW
Notes on the Controller Key Data Read Techniques
1. Timer based key data acquisition
(1) Flowchart
CE=”L”
NO
DO=”L”
YES
Key data read
processing
(2) Timing chart
Key input
Key on
Key on
Key scan
CE
DI
DO
t3
t4
t3
t3
t6
t6
Key
address
t5
t5
Key data read
t6
t5
Key data read request
t7
t7
t7
t7
Controller
Controller
Controller
Controller
Controller
determination
determination
determination
determination
determination
(Key on)
(Key on)
(Key off)
(Key on)
(Key off)
t3 ······· Key scan execution time when the key data agreed for two key scans. (615T[s])
t4 ······· Key scan execution time when the key data did not agree for two key scans and the key scan was executed
again. (1230T[s])
t5 ······· Key address (43H) transfer time
t6 ······· Key data read time
1
1
T= _fOSC = _fCK
(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 t7 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 t7 in this technique must satisfy the following condition.
t7>t4+t5+t6
If a key data read operation is executed when DO is high (DO does not generate a key data read request output), the
read key data (KD1 to KD30) and sleep acknowledge data (SA) will be invalid.
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