*4. Since this output pin is an open-drain output, a pull-up resistor of between 1 and 10 kΩ is required. This pin remains high during the reset period even if a
key data read operation is performed.
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LC75700T
Output pinsState during a reset
KS1 to KS3L
KS4/P4 to KS6/P2L
P1L
DOH *4
To the controller
power supply
To the controller
From the controller
+5 VV
DD
KS4/P4
KI5
KS6/P2
(P1)
(P2)
(P3)
(P4)
P1
OSC
*5.
*6.
*7.
When the power is first applied, it must be initialized by RES = "L".
The DO pin,being an open-drain output, requires a pull-up resistor. Select a resistance (between 1 and 10 kΩ) appropriate
for the capacitance of the external wiring so that signal waveforms are not degraded.
Each of The KS4/P4 to KS6/P2 pins must be set to either the key scan output port or the general-purpose output port.
DO
DI
CL
*
6
Key matrix
(up to 30 keys)
CE
V
SS
KS5/P3
KS3
KS2
KS1
KI4
KI3
KI2
KI1
Used with the backlight
controller or other circuit.
(General-purpose output ports)
RES *5
*7
Note:
Notes on the controller key data read techniques
1. Timer based key data acquisition
(1) Flowchart
(2) Timing chart
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LC75700T
Key data read
processing
YES
NO
DO = "L"
CE = "L"
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 (63H) transfer time
t6: Key data read time
T=
1
fosc
Controller
determination
(Key on)
Key data read request
Key data read
DO
DI
CE
Key onKey on
Key
address
Key scan
Key input
t7t7t7t7
t3t4
t6
t5
t3t3
t6t6
t5t5
Controller
determination
(Key on)
Controller
determination
(Key off)
Controller
determination
(Key on)
Controller
determination
(Key off)
(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 executed the key data read operation.
The period t7 in this technique must satisfy the following condition.
t7 > t4 + t5 + t6
If a keydata read operation is executed when DO is high, the read key data (KD1 to KD30) will be invalid.
2. Interrupt based key data acquisition
(1) Flowchart
(2) Timing chart
Page 15
LC75700T
Key data read
processing
YES
YES
No
DO = "L"
CE = "L"
Wait time of
at least t8
Key OFF
CE = "L"
NO
DO = "H"
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
