PCAL6408AHK115

The PCAL6408AHKX is an 8-bit general purpose I/O expander that provides remote I/Oexpansion for many microcontroller families via the I²C-bus interface.

NXP® I/O expanders provide a simple solution when additional I/Os are needed whilekeeping interconnections to a minimum, for example, in battery-powered mobileapplications for interfacing to sensors, push buttons, keypad, etc. In addition to providinga flexible set of GPIOs, it simplifies interconnection of a processor running at one voltagelevel to I/O devices operating at a different (usually higher) voltage level. The PCAL6408Ahas built-in level shifting feature that makes these devices extremely flexible in mixedsignal environments where communication between incompatible I/O voltages is required.

Its wide VDD range of 1.65 V to 5.5 V on the dual power rail allows seamlesscommunications with next-generation low voltage microprocessors and microcontrollerson the interface side (SDA/SCL) and peripherals at a higher voltage on the port side.

There are two supply voltages for PCAL6408A: VDD(I²C-bus) and VDD(P). VDD(I²C-bus)provides the supply voltage for the interface at the master side (for example, amicrocontroller) and the VDD(P) provides the supply for core circuits and Port P. Thebi-directional voltage level translation in the PCAL6408AHKX is provided through VDD(I²C-bus).VDD(I²C-bus) should be connected to the VDD of the external SCL/SDA lines. This indicatesthe VDD level of the I²C-bus to the PCAL6408A, while the voltage level on Port P of thePCAL6408AHKX is determined by the VDD(P).

The PCAL6408AHKX contains the PCA6408A register set of 8-bit Configuration, Input, Output,and Polarity Inversion registers and additionally, the PCAL6408AHKX has Agile I/O, which areadditional features specifically designed to enhance the I/O. These additional featuresare programmable output drive strength, latchable inputs, programmablepull-up/pull-down resistors, maskable interrupt, interrupt status register, programmableopen-drain or push-pull outputs. The PCAL6408AHKX is a pin-to-pin replacement to thePCA6408A, however, the PCAL6408AHKX powers up with all I/O interrupts masked. Thismask default allows for a board bring-up free of spurious interrupts at power-up.

At power-on, the I/Os are configured as inputs. However, the system master can enablethe I/Os as either inputs or outputs by writing to the I/O configuration bits. The data foreach input or output is kept in the corresponding input or output register. The polarity ofthe Input Port register can be inverted with the Polarity Inversion register, saving externallogic gates. Programmable pull-up and pull-down resistors eliminate the need for discretecomponents.

The system master can reset the PCAL6408AHKX in the event of a time-out or other improperoperation by asserting a LOW in the RESET input. The power-on reset puts the registersin their default state and initializes the I²C-bus/SMBus state machine. The RESET pincauses the same reset/initialization to occur without de-powering the part.

The PCAL6408AHKX open-drain interrupt (INT) output is activated when any input state differsfrom its corresponding Input Port register state and is used to indicate to the systemmaster that an input state has changed.

INT can be connected to the interrupt input of a microcontroller. By sending an interruptsignal on this line, the remote I/O can inform the microcontroller if there is incoming dataon its ports without having to communicate via the I²C-bus. Thus, the PCAL6408AHKX canremain a simple slave device. The input latch feature holds or latches the input pin stateand keeps the logic values that created the interrupt until the master can service theinterrupt. This minimizes the host’s interrupt service response for fast moving inputs.

The device Port P outputs have 25 mA sink capabilities for directly driving LEDs whileconsuming low device current.

One hardware pin (ADDR) can be used to program and vary the fixed I²C-bus addressand allow up to two devices to share the same I²C-bus or SMBus.

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