STMPE1801BJR STMicroelectronics, STMPE1801BJR Datasheet - Page 36

• 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

Keypad controller
36/60
Figure 7.
The keypad rows enabled by the KPC_ROW register are normally 'high', with the
corresponding input pins pulled up by resistors internally. After reset, all the keypad columns
enabled by the KPC_COL register are driven 'low' via weak-pull down resistors. The pull-
down resistors on the column are weaker than the pull-up resistors on the rows. If a key is
pressed, the stronger pull-up drive on the corresponding row overwrites the weaker pull-
down drive on the selected column thus allowing the keyscan controller to sense a "high"
input on the selected column.
Once the keyscan controller senses a "high" on the selected column, the output buffer for
the selected column drives the line low overwriting the pull-up resistor on the corresponding
row. The row that senses the "low" signal enables the key scan controller to decode the key
coordinates (its corresponding row number and column number), save the key data into a
de-bounce buffer if available, confirm if it is a valid key press after de-bouncing, and update
the key data into output data FIFO if valid.
The key press/release detection mechanism is listed below:
1.
2.
3.
When the GPIO is configured as keypad, the ROWS have internal "strong" pull-up and
COLUMNS have internal "weak" pull-down. The initial states of the ROWS are Logic
High and the COLUMNS are Logic Low.
When a keypad is pressed, the corresponding Row and Column form a Resistor
Voltage Divider Network. Since the pull-up resistance of the ROW is stronger than the
pull-down resistance of the COLUMN, the COLUMN is pulled to Logic High.
Once the COLUMN's state changes to Logic High, the state machine initiates a key-
scan cycle and drives the selected COLUMN to Logic Low. A low is detected on the
Keypad controller
Doc ID 17884 Rev 3
STMPE1801