lc75700t Sanyo Semiconductor Corporation, lc75700t Datasheet - Page 10

• Manufacturer Part Number: lc75700t
• Description: Key Scan Ic
• Manufacturer: Sanyo Semiconductor Corporation

Key Scan Operation Functions
1.Key scan timing
2.Key scan operation
Key input 1
Key input 2
Key scan
The key scan period is 288T (s). To reliably determine the on/off state of the keys, this LSI 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 does not agree and a key was pressed at that point, it scans the keys
again. Thus this LSI cannot detect a key press shorter than 615T (s).
•The pins KS1 to KS6 are set to the high or low state by the control data.
•If a key on one of the lines corresponding to a KS1 to KS6 pin which is set high is pressed, the oscillator on the OSC
pin is started and 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 615T (s) (where T = 1/fosc) this LSI 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 this LSI performs
another key scan. Also note that DO being an open-drain output, requires a pull-up resistor (between 1 kΩ and 10 kΩ) .
KS1
KS2
KS3
KS4
KS5
KS6
DO
CE
DI
*2. Not that the high/low states of these pins are determined by the control data, and that key scan output signals are not output
Key on
Serial data transfer
from pins that are set to low .
*2
*2
*2
*2
*2
*2
Key data read request
615T[s]
1
Serial data transfer
2
3
4
Key address (63H)
Key data read
5
6
576T[s]
LC75700T
615T[s]
Serial data transfer
Key data read request
1
2
3
Key data read
Key address
4
5
Key data read request
615T[s]
6
*2
*2
*2
*2
*2
*2
Key address
Key data read
T=
No. 7632-10/16
fosc
T=
1
fosc
1