Classes
class	I2cInterface
	CRTP-based template interface for I2C bus operations. More...

class	PCAL95555
	Driver for the PCA9555 / PCAL9555A / PCAL95555AHF I²C GPIO expander. More...

struct	PinReadResult
	Fixed-capacity result container for multi-pin read operations. More...

Enumerations
enum class	Pcal95555Reg : uint8_t { INPUT_PORT_0 = 0x00 , INPUT_PORT_1 = 0x01 , OUTPUT_PORT_0 = 0x02 , OUTPUT_PORT_1 = 0x03 , POLARITY_INV_0 = 0x04 , POLARITY_INV_1 = 0x05 , CONFIG_PORT_0 = 0x06 , CONFIG_PORT_1 = 0x07 , DRIVE_STRENGTH_0 = 0x40 , DRIVE_STRENGTH_1 = 0x41 , DRIVE_STRENGTH_2 = 0x42 , DRIVE_STRENGTH_3 = 0x43 , INPUT_LATCH_0 = 0x44 , INPUT_LATCH_1 = 0x45 , PULL_ENABLE_0 = 0x46 , PULL_ENABLE_1 = 0x47 , PULL_SELECT_0 = 0x48 , PULL_SELECT_1 = 0x49 , INT_MASK_0 = 0x4A , INT_MASK_1 = 0x4B , INT_STATUS_0 = 0x4C , INT_STATUS_1 = 0x4D , OUTPUT_CONF = 0x4F }
	Register addresses for the PCA9555 / PCAL9555A I/O expander chips. More...

enum class	GPIODir : uint8_t { Input = 1 , Output = 0 }

enum class	Polarity : uint8_t { Normal = 0 , Inverted = 1 }

enum class	DriveStrength : uint8_t { Level0 = 0 , Level1 = 1 , Level2 = 2 , Level3 = 3 }

enum class	OutputMode : uint8_t { PushPull = 0 , OpenDrain = 1 }

enum class	InterruptEdge : uint8_t { Rising = 1 , Falling = 2 , Both = 3 }

enum class	InterruptState : uint8_t { Enabled = 0 , Disabled = 1 }

enum class	Error : uint16_t { None = 0 , InvalidPin = 1 << 0 , InvalidMask = 1 << 1 , I2CReadFail = 1 << 2 , I2CWriteFail = 1 << 3 , UnsupportedFeature = 1 << 4 , InvalidAddress = 1 << 5 }

enum class	ChipVariant : uint8_t { Unknown = 0 , PCA9555 = 1 , PCAL9555A = 2 }
	Identifies the detected or user-specified chip variant. More...

enum class	CtrlPin : uint8_t { INTN = 0 , RSTN }
	Identifies the hardware control pins of the PCAL95555. More...

enum class	GpioSignal : uint8_t { INACTIVE = 0 , ACTIVE = 1 }
	Abstract signal level for control pins. More...

Functions
constexpr Error	operator\| (Error lhs, Error rhs) noexcept
	Combine two Error flags.

constexpr Error	operator& (Error lhs, Error rhs) noexcept
	Intersect two Error flags.

constexpr Error	operator~ (Error e) noexcept
	Complement an Error flag (useful with ClearErrorFlags).

const char *	GetDriverVersion () noexcept

Enumeration Type Documentation

◆ ChipVariant

enum class pcal95555::ChipVariant : uint8_t

strong

Identifies the detected or user-specified chip variant.

The driver supports both the standard PCA9555 and the enhanced PCAL9555A. The variant is auto-detected during initialization by probing an Agile I/O register. It can also be forced via the constructor to skip detection.

Enumerator
Unknown	Not yet detected (pre-initialization)
PCA9555	Standard PCA9555 (registers 0x00-0x07 only)
PCAL9555A	NXP PCAL9555A with Agile I/O (registers 0x00-0x07 + 0x40-0x4F)

Examples: /home/runner/work/hf-pcal95555-driver/hf-pcal95555-driver/inc/pcal95555.hpp.

◆ CtrlPin

enum class pcal95555::CtrlPin : uint8_t

strong

Identifies the hardware control pins of the PCAL95555.

Used with GpioSet() / GpioRead() to control or read the IC's dedicated GPIO pins through the I2cInterface.

INTN: Active-low interrupt output (read-only via GpioRead)

The PCA9555 and PCAL9555A have no reset input (PCAL9555A data sheet Rev. 2, table 3; PCA9555 Rev. 10, table 3): the only reset is power-on reset, and PCAL95555::ResetToDefault() rewrites the power-up register values instead. RSTN is kept only so existing ports still compile.

Enumerator
INTN	Interrupt output (active-low, open-drain, read-only)
RSTN	No such pin on these parts; never driven by the driver.

Examples: /home/runner/work/hf-pcal95555-driver/hf-pcal95555-driver/inc/pcal95555_i2c_interface.hpp.

◆ DriveStrength

enum class pcal95555::DriveStrength : uint8_t

strong

Output drive strength levels (00=¼, 11=full).

Enumerator
Level0
Level1
Level2
Level3

Examples: /home/runner/work/hf-pcal95555-driver/hf-pcal95555-driver/inc/pcal95555.hpp.

◆ Error

enum class pcal95555::Error : uint16_t

strong

Error conditions reported by the driver.

Enumerator
None
InvalidPin	Provided pin index out of range.
InvalidMask	A mask-form call got a mask that selects no pin (0)
I2CReadFail	An I2C read operation failed.
I2CWriteFail	An I2C write operation failed.
UnsupportedFeature	Feature requires PCAL9555A but chip is PCA9555.
InvalidAddress	Provided I2C address is out of valid range (0x20-0x27)

Examples: /home/runner/work/hf-pcal95555-driver/hf-pcal95555-driver/inc/pcal95555.hpp.

◆ GPIODir

enum class pcal95555::GPIODir : uint8_t

strong

GPIO direction (1=input, 0=output).

Enumerator
Input
Output

Examples: /home/runner/work/hf-pcal95555-driver/hf-pcal95555-driver/inc/pcal95555.hpp.

◆ GpioSignal

enum class pcal95555::GpioSignal : uint8_t

strong

Abstract signal level for control pins.

Decouples the driver's intent from the physical pin polarity.

Enumerator
INACTIVE	Pin function is deasserted.
ACTIVE	Pin function is asserted.

Examples: /home/runner/work/hf-pcal95555-driver/hf-pcal95555-driver/inc/pcal95555_i2c_interface.hpp.

◆ InterruptEdge

enum class pcal95555::InterruptEdge : uint8_t

strong

Interrupt edge trigger type.

Enumerator
Rising	Trigger on rising edge (LOW to HIGH)
Falling	Trigger on falling edge (HIGH to LOW)
Both	Trigger on both edges.

Examples: /home/runner/work/hf-pcal95555-driver/hf-pcal95555-driver/inc/pcal95555.hpp.

◆ InterruptState

enum class pcal95555::InterruptState : uint8_t

strong

Interrupt enable/disable state.

Enumerator
Enabled	Interrupt enabled (mask bit = 0)
Disabled	Interrupt disabled/masked (mask bit = 1)

Examples: /home/runner/work/hf-pcal95555-driver/hf-pcal95555-driver/inc/pcal95555.hpp.

◆ OutputMode

enum class pcal95555::OutputMode : uint8_t

strong

Output mode (push-pull vs open-drain).

Enumerator
PushPull
OpenDrain

Examples: /home/runner/work/hf-pcal95555-driver/hf-pcal95555-driver/inc/pcal95555.hpp.

◆ Pcal95555Reg

enum class pcal95555::Pcal95555Reg : uint8_t

strong

Register addresses for the PCA9555 / PCAL9555A I/O expander chips.

PCAL95555 register map (all control registers).

The register map is split into two banks:

Standard PCA9555 registers (0x00-0x07) - Supported by both PCA9555 and PCAL9555A:

Input/Output registers (0x00-0x03): Read inputs and control outputs
Configuration registers (0x04-0x07): Configure polarity and port direction

PCAL9555A Agile I/O registers (0x40-0x4F) - PCAL9555A only:

Drive strength registers (0x40-0x43): Control output drive strength
Input/Pull registers (0x44-0x49): Configure input latching and pull-up/down
Interrupt registers (0x4A-0x4D): Manage interrupt mask and status
Output configuration (0x4F): Push-pull vs open-drain per port

Each register controls 8 pins, with PORT_0 handling pins 0-7 and PORT_1 handling pins 8-15.

Note: Accessing Agile I/O registers on a standard PCA9555 will result in I2C NACK. The driver auto-detects the chip variant and guards these registers accordingly.

Enumerator
INPUT_PORT_0	Input port 0 (read-only) [PCA9555 + PCAL9555A].
INPUT_PORT_1	Input port 1 (read-only) [PCA9555 + PCAL9555A].
OUTPUT_PORT_0	Output port 0 [PCA9555 + PCAL9555A].
OUTPUT_PORT_1	Output port 1 [PCA9555 + PCAL9555A].
POLARITY_INV_0	Polarity inversion port 0 [PCA9555 + PCAL9555A].
POLARITY_INV_1	Polarity inversion port 1 [PCA9555 + PCAL9555A].
CONFIG_PORT_0	Configuration (direction) port 0 [PCA9555 + PCAL9555A].
CONFIG_PORT_1	Configuration (direction) port 1 [PCA9555 + PCAL9555A].
DRIVE_STRENGTH_0	Output drive strength port 0 low nibble [PCAL9555A only].
DRIVE_STRENGTH_1	Output drive strength port 0 high nibble [PCAL9555A only].
DRIVE_STRENGTH_2	Output drive strength port 1 low nibble [PCAL9555A only].
DRIVE_STRENGTH_3	Output drive strength port 1 high nibble [PCAL9555A only].
INPUT_LATCH_0	Input latch port 0 [PCAL9555A only].
INPUT_LATCH_1	Input latch port 1 [PCAL9555A only].
PULL_ENABLE_0	Pull-up/pull-down enable port 0 [PCAL9555A only].
PULL_ENABLE_1	Pull-up/pull-down enable port 1 [PCAL9555A only].
PULL_SELECT_0	Pull-up/pull-down selection port 0 [PCAL9555A only].
PULL_SELECT_1	Pull-up/pull-down selection port 1 [PCAL9555A only].
INT_MASK_0	Interrupt mask port 0 [PCAL9555A only].
INT_MASK_1	Interrupt mask port 1 [PCAL9555A only].
INT_STATUS_0	Interrupt status port 0 (read-only) [PCAL9555A only].
INT_STATUS_1	Interrupt status port 1 (read-only) [PCAL9555A only].
OUTPUT_CONF	Output port configuration [PCAL9555A only].

Examples: /home/runner/work/hf-pcal95555-driver/hf-pcal95555-driver/inc/pcal95555.hpp.

◆ Polarity

enum class pcal95555::Polarity : uint8_t

strong

Input polarity inversion (0=normal, 1=inverted).

Enumerator
Normal
Inverted

Examples: /home/runner/work/hf-pcal95555-driver/hf-pcal95555-driver/inc/pcal95555.hpp.

Function Documentation

◆ GetDriverVersion()

const char * pcal95555::GetDriverVersion ( )

inlinenoexcept

Examples: /home/runner/work/hf-pcal95555-driver/hf-pcal95555-driver/inc/pcal95555.hpp.

◆ operator&()

constexpr Error pcal95555::operator&	(	Error	lhs,
		Error	rhs
	)

inlineconstexprnoexcept

Intersect two Error flags.

◆ operator|()

constexpr Error pcal95555::operator\|	(	Error	lhs,
		Error	rhs
	)

inlineconstexprnoexcept

Combine two Error flags.

◆ operator~()

constexpr Error pcal95555::operator~ ( Error e )

inlineconstexprnoexcept

Complement an Error flag (useful with ClearErrorFlags).

Classes

Enumerations

Functions

Enumeration Type Documentation

◆ ChipVariant

◆ CtrlPin

◆ DriveStrength

◆ Error

◆ GPIODir

◆ GpioSignal

◆ InterruptEdge

◆ InterruptState

◆ OutputMode

◆ Pcal95555Reg

◆ Polarity

Function Documentation

◆ GetDriverVersion()

◆ operator&()

◆ operator|()

◆ operator~()