LC75817E Datasheet, PDF (22/43 Pages) Sanyo Semicon Device – 1/8 to 1/10 Duty Dot Matrix LCD Display Controller/Driver with Key Input Function

LC75817E, 75817W
Key Scan Operation Functions
• Key scan timing
The key scan period is 2304T(s). To reliably determine the on/off state of the keys, the LC75817E/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) 4800T(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 LC75817E/W cannot detect a key press shorter than 4800T(s).
KS1
*18
KS2
*18
KS3
*18
KS4
*18
KS5
*18
KS6
*18
*18
*18
*18
T= ¹
fosc
*18
*18
*18
4608T(s)
Key on
Note: *18. Note that the high/low states of these pins are determined by the “set key scan output state” instruction, and that key scan output signals are not
output from pins that are set to low.
• In normal mode
• _{The pins KS1 to KS6 are set to high or low with the “set key scan output state” instruction.}
• _{If a key on one of the lines corresponding to a KS1 to KS6 pin which is set high is pressed, a key scan is started and}
the 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 4800T(s) (Where T= —fo1—sc ) the LC75817E/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 LC75817E/W}
performs another key scan. Also note that DO, being an open-drain output, requires a pull-up resistor (between 1 and
10 kΩ).
Key input 1
Key input 2
Key scan
CE
DI
4800T(s)
Serial data
transfer
Serial data Key address
transfer
(43H)
4800T(s)
Serial data
transfer
Key
address
4800T(s)
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
No. 6144-22/43