TWI Keypad Card This card only utilizes PCF8574 Remote 8-bit I/O expander for I2C (Inter-Integrated Circuit)-bus This device consists of an 8-bit quasi-bidirectional port and an I2C (Inter-Integrated Circuit)-bus interface. The PCF8574 has a low current consumption and includes latched outputs with high current drive capability for directly driving LEDs. It also possesses an interrupt line (INT) which can be connected to the interrupt logic of the Blackfin Processor. By sending an interrupt signal on this line, the remote I/O can inform the Blackfin Processor if there is incoming data on its ports without having to communicate via the I2C (Inter-Integrated Circuit)-bus. This means that the PCF8574 can remain a simple slave device. It's therefore perfectly suited to scan a Keypad 4x4 matrix, resulting in 8-bit. One GPIO (General Purpose Input/Output) is used to inform Blackfin - that data is available. While definitely! the user still has the finger on the button. Blackfin TWI Keypad Driver