STMPE1601 datasheet(52/58 Pages) STMICROELECTRONICS

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Keypad combination key registers

STMPE1601

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Resistance

The maximum resistance between keypad outputs and inputs, inclusive of switch resistance,

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

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 the 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

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 EN_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 EN_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.

Ghost key handling

The 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 STMPE1601 allows the

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

the key matrix.

The ghost key is only possible if 3 keys are pressed and held down together in a keypad

matrix. If 3 keys are reported by the STMPE1601 keypad controller, it indicates a potential

ghost key situation. The system may check for the possibility of a 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.

A 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 keys.

Key detection priority

A dedicated key is always detected, if this is enabled. When a special function key is

detected, the matrix key scanning on the same input line is disabled.

Up to 3 matrix keys can be detected. Matrix keys that fall on activated special function keys

will not be counted.

As a result of these priority rules, a matrix key is ignored by the keypad controller when the

special function key on the same input line is detected, even if the matrix key is being

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