STMPE2403 datasheet(54/63 Pages) STMICROELECTRONICS

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Keypad controller

STMPE2403

54/63

12.8.1

Resistance

Maximum resistance between keypad output and keypad input, inclusive of switch

resistance, protection circuit resistance and connection, must be less than 3.2 K

Ω

12.8.2

Using the keypad controller

It is not necessary to explicitly enable the internal pull-up and direction by configuring the GPIO control

registers. Once a GPIO is enabled for keypad function, its internal pull-up and direction is controlled

automatically.

The scanning of column inputs should then be enabled for those GPIO ports that are

configured as keypad inputs by writing ‘1’s to the corresponding bits in the KPC_col register.

If any of the first three column inputs is to be used as dedicated key input, the corresponding

bits in the KPC_ctrl_msb register should be set to ‘1’. The bits in the KPC_row_msb and

KPC_row_lsb registers should also be set correctly to enable the row output scanning for

the corresponding GPIO ports programmed as keypad outputs.

The scan count and de-bounce count should also be programmed into the keypad control

registers before enabling the keypad controller operation. To enable the keypad controller

operation, the Enable_KPC bit in the system control register must be set to ‘1’ to provide the

required clock signals. The keypad controller will then start its operation by setting the

SCAN bit in the KPC_ctrl_lsb register to ‘1’.

The keypad controller operation can be disabled by setting the SCAN bit back to ‘0’. To

further reduce the power consumption, the clock signals can be cut off from the keypad

controller by setting the Enable_KPC bit to ‘0’.

As long as there is any un-read key-press in the keypad controller buffer, the KPC interrupt

will always be asserted.

12.8.3

Ghost Key Handling

Ghost key is an inherent in keypad matrix that is not equipped with a diode at each of the

keys. While it is not possible to avoid ghost key occurrence, the STMPE2403 allow the

detection of possible ghost key by the capability of detecting 3 simultaneous key-presses in

the key matrix.

Ghost key is only possible if 3 keys are pressed and held down together in a keypad matrix.

If 3 keys are reported by STMPE2403 keypad controller, it indicates a potential ghost key

situation. The system may check for possibility of ghost key by analyzing the coordinates of

the 3 keys. If the 3 keys form 3 corners of a rectangle, it could be a ghost key situation.

Ghost key may also occur in the Special Function Keys. The keypad controller does not

attempt to avoid the occurrence of ghost keys. However, the system should be aware that if

more than one special function key is reported, then there is a possibility of ghost key.

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