STMPE1801BJR STMicroelectronics, STMPE1801BJR Datasheet - Page 51

• Manufacturer Part Number: STMPE1801BJR
• Description: Touch Screen Converters & Controllers Xpander Logic 18-Bit 18 GPIO 1.65 to 3.6V
• Manufacturer: STMicroelectronics

Specifications of STMPE1801BJR

• Rohs: yes
• Input Type: 1 Keypad
• Data Rate: 400 kbps
• Resolution: 18 bit
• Interface Type: I2C
• Supply Voltage: 1.65 V to 3.6 V
• Supply Current: 28 uA
• Operating Temperature: - 40 C to + 85 C
• Package / Case: CSP-25
• Maximum Operating Temperature: + 85 C
• Minimum Operating Temperature: - 40 C
• Mounting Style: SMD/SMT
• Supply Voltage - Max: 3.6 V
• Supply Voltage - Min: 1.65 V

STMPE1801
11.5
11.5.1
11.5.2
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
register. It is the host responsibility to read the KPC Data register to access all key-press
data.
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.
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".
Doc ID 17884 Rev 3
Keypad controller
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