STMPE1801BJR datasheet(37/60 Pages) STMICROELECTRONICS

37 / 60 page

STMPE1801

Keypad controller

Doc ID 17884 Rev 3

37/60

key-press ROW. This is because the row and column node of key press are shorted

together.

The state machine continues to poll while the key is still pressed and is reinitialized

once all the keys are released.

The key detection sequence is described below:

The column outputs are initially not driven.

Then the row inputs are checked for any special function keys.

Next, the columns are checked for any normal key presses.

With the internal pull-down resistor on the columns, the column senses a logic low. But

when there is a normal key press, the pull up on the row and pull down on the column

forms a resistor voltage divider. Since the pull up resistor is sized much smaller than

the pull down resistor, the voltage on the column is pulled to logic high state.

Then only the configured columns that sensed a high are driven low in turn and check

for normal key presses.

This eliminates the need to drive columns that do not have any key press. This in turn

reduces the switching amount and hence the reduction in noise and EMI.

Also the 4 mA IO during GPIO mode is 1 mA in keypad mode.

STMPE1801BJR Fiches technique(PDF) 37 Page - STMicroelectronics