BU97540KV-M Datasheet, PDF (43/70 Pages) Rohm – Multi-function Segment Drivers

BU97540KV-M
Controller Key Data Read Techniques
When the controller receives a key data read request from BU97540KV-M, it performs a key data read acquisition operation
using either the Timer Based Key Data Acquisition or the Interrupt Based Key Data Acquisition.
Timer Based Key Data Acquisition Technique
Under the Timer Based Key Data Acquisition Technique, the controller uses a timer to determine the states of the keys
(ON or OFF) and read the key data. Please refer to the flowchart below.
SCE ＝ 「L 」
NO
SDO ＝ 「L 」
YES
Key data read
processing
Key data read processing: Refer to “Serial Data Output”
Figure 20. Flowchart
In this technique, the controller uses a timer to determine key on/off states and read the key data. The controller must check
the SDO state when SCE is low every t7 period without fail. If SDO 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 SDO is high, the read key data (KD1 to KD20) and sleep acknowledge data
(SA) will be invalid.
Key Input
Key on
Key on
Key scan
t3
t4
t3
t3
SCE
t6
t6
t6
SDI
SDO
t5
t5
t5
Key data read
Key data read request
t7
t7
t7
t7
Controller determination Controller determination Controller determination Controller determination Controller determination
(key on)
(key on)
(key on)
(key on)
(key on)
t3: Key scan execution time when the key data agreed for two key scans. (9904T(s))
t4: Key scan execution time when the key data did not agree for two key scans and the key scan was executed again.
(19808T(s)) T = 1 / fosc
t5: Key address (43H) transfer time
t6: Key data read time
Figure 21. Timer based key data read operation
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