ML9092-01TB datasheet(43/66 Pages) OKI

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FEDL9092-01

OKI Semiconductor

ML9092-01/02/03/04

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Key Scan

The key scanning starts when a key switch is pressed on and ends after all key switches are detected to be off.

After the key switch is turned on, when the same key is pressed for two cycles or more, the level of the KREQ

signal changes from a “L” to “H” level. In the same manner, the level of the KREQ signal changes from “H” to

“L” two cycles after all key switches are turned off.

This signal can be used as a flag. To use it as a flag, start key-scan reading when the KREQ signal has changed

from “L” to “H.”

While the KREQ signal is at a “H” level, carry out key-scan reading periodically. Carry out key scan reading also

when the KREQ signal has changed from “H” to “L”.

The KREQ signal (the KREQ signal that is sent when the key switch is turned on) is reset when all key switches are

detected to be off or when a “L” level is applied to the

RESET pin.

Scanning stops

Key switch OFF

Key data reading

starts

Key switch ON.

Scanning starts.

KREQ

Key switch

R0/C0

R1/C1

R2/C2

R3/C3

R4/C4

Notes:

Even when the KREQ signal changes from “L” to “H”, chattering for more than one key scan cycle is

not absorbed. This should be handled by multiple data reads by software.

How simultaneous depression of two keys is processed should be handled by software.

When three or more key switches are pressed at the same time, the device may recognize that

key(s) that has not been actually pressed has been pressed. Therefore, to recognize simultaneous

depression of three or more key switches, add a diode in series to each key (see Figures 1 and 2).

To ignore simultaneous depression of three or more key switches, a program may be required to

ignore all key data which contains three or more consecutive “1” values.

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