BU97501KV Datasheet, PDF (11/33 Pages) Rohm – Integrated RAM for display data

BU97501KV
Datasheet
Key Scan Operation
Key Scan Timing
The key scan period is 288T(s). To reliably determine the on/off state of the keys, the BU97501KV 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 is pressed at that point, it scans the keys
again. Thus, BU97501KV cannot detect a key press shorter than 615T(s).
KS1 ^{* 1}
1
*
KS2 ^*
2
2
*
KS3 ^*
3
3
*
KS4 ^*
4
4
*
KS5 ^*
5
5
*
KS6
6
6
57⁹²6¹T^6T[S^[S]^]
1
T=
fosc
Figure 10. Key Scan Timing
Normal Mode
KS1/S42 - KS6/S47 pins are set high.
When a key 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 615 T(s) (Where T=1/fosc (When External clock input, fosc is a quarter of external
clock)), the BU97501KV 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 CSB is ”L” 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 BU97501KV performs
another key scan. Also note that DO can be controlled to be an open-drain output or a CMOS output. If set to be an
open-drain output, a pull-up resistor (between 1 and 10KΩ) is required.
Figure 11. Key scan operation in normal mode
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11.Apr.2014 Rev.004