STMPE1801 datasheet(51/60 Pages) STMICROELECTRONICS

51 / 60 page

STMPE1801

Keypad controller

Doc ID 17884 Rev 3

51/60

11.5

Using the keypad controller

It is not necessary to explicitly enable the internal pull-up, pull-down and direction by

configuring the GPIO control registers. Once a GPIO is enabled for the keypad function, its

internal pull-up, pull-down and direction is controlled automatically.

The scanning of row 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_ROW register. If any of

the first four row inputs is to be used as dedicated key input, the corresponding bits in the

KPC_CTRL_MID register should be set to '1'. The bits in the KPC_COL_HIGH and

KPC_COL_LOW registers should also be set correctly to enable the column 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 SCAN bit in the KPC_CTRL_LOW register must be set to '1'. The keypad

controller operation can be disabled by setting the SCAN bit back to '0'. The KPC interrupt

can be cleared upon status bit read, even if there is unread key-press in the KPC Data

data.

11.5.1

Ghost key handling

The ghost key is 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 STMPE1801 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 STMPE1801 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.

11.5.2

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

are not 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

pressed down before the special function key. Hence, when a matrix is reported "key-down"

and it is being held down while the corresponding special function is being pressed, a "no

key" status is reported for the matrix key when the special function key is reported "key-

down". If the matrix key is released while the special function key is still being held down, no

"key-up" will be reported for the matrix key. On the other hand, if the matrix key is released

after the special function key is reported "key-up", then a new "key-down" is reported for the

matrix key, followed by "key-up".

STMPE1801 数据表(PDF) 51 Page - STMicroelectronics

STMPE1801 数据表(HTML) 51 Page - STMicroelectronics

Html Pages

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

数据表下载