Hardware

AN3245

10/19

Doc ID 17747 Rev 1

1.4.2

Dedicated keys

The following is the configuration of the maximum 4 dedicated keys. Four of the row inputs

(GPIO_0, GPIO_1, GPIO_2, and GPIO_3 pins) can be configured as dedicated keys

through the setting of Dkey0~3 bits of the KPC_CTRL register. The dedicated keys function

supports up to 4 simultaneous key presses in the applications.

Figure 9.

Dedicated keys configurations

1.4.3

Combination keys

The 80 matrix keys can be programmed into a 3 combination key which when pressed

simultaneously wakes up the keypad controller and sends an interrupt to the host system.

This feature can be used to implement the <Ctrl> + <Alt> + <Delete> function.

Please refer to Section 1.4.4 for care and handling of ghost keys.

1.4.4

Ghost keys handling

The ghost key is an inherent 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 through 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 may 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.

●

Three simultaneous key presses with ghost key event

–

STMPE1801 stores and reports the 3 keys data

–

System host reads key coordinates that form a 90° corner of a rectangle. System

host should be aware of the possible ghost key event in this condition and

discard/ignore the key data.