LC75886PW Datasheet, PDF (31/36 Pages) ON Semiconductor – 1/4 and 1/3-Duty LCD Display Driver

2. Interrupt based key data acquistion
(1) Flowchart
CE=”L”
NO
DO=”L”
YES
Key data read
processing
Wait for
at least t8
CE=”L”
NO
DO=”H”
YES
Key OFF
LC75886PW
(2) Timing chart
Key input
Key on
Key on
Key scan
CE
DI
DO
t3
t3
t4
t3
t6
Key
address
t5
Key data read
t6
t5
t6
t5
Key data read request
Controller
determination
(Key on)
t8
Controller
determination
(Key off)
Controller
determination
(Key on)
t8
Controller
determination
(Key on)
t6
t5
t8
Controller
determination
(Key on)
t8
Controller
determination
(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 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 (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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