LC75857E Datasheet, PDF (18/39 Pages) Sanyo Semicon Device – CMOS IC 1/3, 1/4 Duty LCD Display Drivers with Key Input Function

LC75857E, LC75857W
Key Scan Operation Functions
1. Key scan timing
The key scan period is 288T(s). To reliably determine the on/off state of the keys, the LC75857E/W scans the keys
twice and determines that a key has been pressed when the key data agrees. It outputs a key data read request (a low
level on DO) 615T(s) after starting a key scan. If the key data dose not agree and a key was pressed at that point, it
scans the keys again. Thus the LC75857E/W cannot detect a key press shorter than 615T(s).
KS1 *3 1
1
*3
KS2 *3
2
2
*3
KS3 *3
KS4 *3
3
4
3
4
*3
*3
T=
1
fosc
=
1
fCK
KS5 *3
5
5
*3
KS6 *3
6
6 *3
Key on
576T[s]
Note: *3. These are set to the high or low level by the KC0 to KC2 bits in the control data. Key scan output signals are not output from pins that are set to the low level.
2. Normal mode, when key scan operations are enabled
• The KS1 to KS6 pins are set to the high or low level by the KC0 to KC2 bits in the control data. (See the
description of the control data.)
• When any key on the lines corresponding to KS1 to KS6 pin which is set high is pressed, a key scan is
performed. Keys are scanned until all keys are released. Multiple key presses are recognized by determining
whether multiple key data bits are set.
• If a key is pressed for longer than 615 T (s) (Where T= —fo1—sc = —f_C^1—_K ) the LC75857E/W outputs a key data read
request (a low level on DO) to the controller. The controller acknowledges this request and reads the key data.
However, if CE is high during a serial data transfer, DO will be set high.
• After the controller reads the key data, the key data read request is cleared (DO is set high) and the LC75857E/W
performes another key scan. Also note that DO, being an open-drain output, requires a pull-up resistor (between 1
to 10 kΩ).
Key input 1
Key input 2
Key scan
615T[s]
CE
Serial data transfer
(KSC = 0)
DI
Serial data transfer
(KSC = 0)
615T[s]
Serial data transfer
Key address (43H)
(KSC = 0)
615T[s]
Key address
Key address
DO
Key data read request
Key data read
Key data read
Key data read
Key data read request
Key data read request
T=
1
fosc
=
1
fCK
No. 7980-18/39