Complete reference documentation for all public methods and types in the PCAL95555 driver.

Source Code

Main Header: inc/pcal95555.hpp
Kconfig Macros: inc/pcal95555_kconfig.hpp (compile-time configuration, included by main header)
Implementation: src/pcal95555.ipp

Core Class

`PCAL95555<I2cType>`

Main driver class for interfacing with the PCA9555 and PCAL9555A I/O expanders. The chip variant is auto-detected during initialization. PCAL9555A-specific features (pull resistors, drive strength, input latch, interrupt mask/status, output mode) return false and set Error::UnsupportedFeature when a standard PCA9555 is detected.

Template Parameter: I2cType - Your I2C interface implementation (must inherit from pcal95555::I2cInterface<I2cType>)

Location: inc/pcal95555.hpp

Constructors:

Constructor 1: Using address pin levels

PCAL95555(I2cType* bus, bool a0_level, bool a1_level, bool a2_level,

ChipVariant variant = ChipVariant::Unknown);

Parameters:

bus: Pointer to your I2C interface implementation
a0_level: Initial state of A0 pin (true = HIGH/VDD, false = LOW/GND)
a1_level: Initial state of A1 pin (true = HIGH/VDD, false = LOW/GND)
a2_level: Initial state of A2 pin (true = HIGH/VDD, false = LOW/GND)
variant: Optional chip variant override. Default ChipVariant::Unknown enables auto-detection. Set to ChipVariant::PCA9555 or ChipVariant::PCAL9555A to skip detection.

Constructor 2: Using I2C address directly

explicit PCAL95555(I2cType* bus, uint8_t address,

ChipVariant variant = ChipVariant::Unknown);

Parameters:

bus: Pointer to your I2C interface implementation
address: 7-bit I2C address (0x20 to 0x27). Address bits are calculated automatically.
variant: Optional chip variant override (same as above).

Description: Both constructors use lazy initialization – no I2C traffic occurs in the constructor. Initialization (including chip variant detection) happens on first method call or explicit EnsureInitialized(). The address is calculated from A0-A2 levels or used directly. SetAddressPins() is called if supported by the I2C interface.

Examples:

// Using pin levels - auto-detect chip variant (default)
PCAL95555 driver1(bus, false, false, false);
 
// Using address directly - auto-detect
PCAL95555 driver2(bus, 0x20);
 
// Force PCA9555 mode (skip Agile I/O detection probe)
PCAL95555 driver3(bus, 0x20, ChipVariant::PCA9555);
 
// Force PCAL9555A mode
PCAL95555 driver4(bus, false, false, false, ChipVariant::PCAL9555A);

Location: inc/pcal95555.hpp

Methods

Initialization

Method	Signature	Location
`EnsureInitialized()`	`bool EnsureInitialized()`	`src/pcal95555.ipp`
`ResetToDefault()`	`void ResetToDefault()`	`src/pcal95555.ipp`
`InitFromConfig()`	`void InitFromConfig()`	`src/pcal95555.ipp`

Pin Direction

Method	Signature	Location
`SetPinDirection()`	`bool SetPinDirection(uint16_t pin, GPIODir dir)`	`src/pcal95555.ipp`
`SetDirections()`	`bool SetDirections(std::initializer_list<std::pair<uint16_t, GPIODir>> configs)`	`src/pcal95555.ipp`
`SetMultipleDirections()`	`bool SetMultipleDirections(uint16_t mask, GPIODir dir)`	`src/pcal95555.ipp`

Pin I/O

Method	Signature	Location
`ReadPin()`	`bool ReadPin(uint16_t pin)`	`src/pcal95555.ipp`
`ReadPins()`	`std::vector<std::pair<uint16_t, bool>> ReadPins(std::initializer_list<uint16_t> pins)`	`src/pcal95555.ipp`
`WritePin()`	`bool WritePin(uint16_t pin, bool value)`	`src/pcal95555.ipp`
`WritePins()`	`bool WritePins(std::initializer_list<std::pair<uint16_t, bool>> configs)`	`src/pcal95555.ipp`
`TogglePin()`	`bool TogglePin(uint16_t pin)`	`src/pcal95555.ipp`

Pull-up/Pull-down (PCAL9555A only)

‍Note: These methods return false and set Error::UnsupportedFeature on PCA9555.

Method	Signature	Location
`SetPullEnable()`	`bool SetPullEnable(uint16_t pin, bool enable)`	`src/pcal95555.ipp`
`SetPullEnables()`	`bool SetPullEnables(std::initializer_list<std::pair<uint16_t, bool>> configs)`	`src/pcal95555.ipp`
`SetPullDirection()`	`bool SetPullDirection(uint16_t pin, bool pull_up)`	`src/pcal95555.ipp`
`SetPullDirections()`	`bool SetPullDirections(std::initializer_list<std::pair<uint16_t, bool>> configs)`	`src/pcal95555.ipp`

Drive Strength (PCAL9555A only)

‍Note: These methods return false and set Error::UnsupportedFeature on PCA9555.

Method	Signature	Location
`SetDriveStrength()`	`bool SetDriveStrength(uint16_t pin, DriveStrength level)`	`src/pcal95555.ipp`
`SetDriveStrengths()`	`bool SetDriveStrengths(std::initializer_list<std::pair<uint16_t, DriveStrength>> configs)`	`src/pcal95555.ipp`

Interrupts

‍Note: ConfigureInterrupt, ConfigureInterrupts, ConfigureInterruptMask, and GetInterruptStatus require PCAL9555A and return false/0 with Error::UnsupportedFeature on PCA9555. The remaining interrupt methods (callbacks, handler) work on both variants – on PCA9555, HandleInterrupt() uses change-detection (comparing current vs. previous pin states) instead of the hardware interrupt status register.

Method	Signature	PCAL9555A?	Location
`ConfigureInterrupt()`	`bool ConfigureInterrupt(uint16_t pin, InterruptState state)`	Yes	`src/pcal95555.ipp`
`ConfigureInterrupts()`	`bool ConfigureInterrupts(std::initializer_list<std::pair<uint16_t, InterruptState>> configs)`	Yes	`src/pcal95555.ipp`
`ConfigureInterruptMask()`	`bool ConfigureInterruptMask(uint16_t mask)`	Yes	`src/pcal95555.ipp`
`GetInterruptStatus()`	`uint16_t GetInterruptStatus()`	Yes	`src/pcal95555.ipp`
`RegisterPinInterrupt()`	`bool RegisterPinInterrupt(uint16_t pin, InterruptEdge edge, std::function<void(uint16_t, bool)> callback)`	No	`src/pcal95555.ipp`
`UnregisterPinInterrupt()`	`bool UnregisterPinInterrupt(uint16_t pin)`	No	`src/pcal95555.ipp`
`SetInterruptCallback()`	`void SetInterruptCallback(const std::function<void(uint16_t)>& callback)`	No	`src/pcal95555.ipp`
`RegisterInterruptHandler()`	`bool RegisterInterruptHandler()`	No	`src/pcal95555.ipp`
`HandleInterrupt()`	`void HandleInterrupt()`	No	`src/pcal95555.ipp`

Output Mode (PCAL9555A only)

‍Note: Returns false and sets Error::UnsupportedFeature on PCA9555.

Method	Signature	Location
`SetOutputMode()`	`bool SetOutputMode(bool port_0_open_drain, bool port_1_open_drain)`	`src/pcal95555.ipp`

Polarity

Method	Signature	Location
`SetPinPolarity()`	`bool SetPinPolarity(uint16_t pin, Polarity polarity)`	`src/pcal95555.ipp`
`SetPolarities()`	`bool SetPolarities(std::initializer_list<std::pair<uint16_t, Polarity>> configs)`	`src/pcal95555.ipp`
`SetMultiplePolarities()`	`bool SetMultiplePolarities(uint16_t mask, Polarity polarity)`	`src/pcal95555.ipp`

Input Latch (PCAL9555A only)

‍Note: These methods return false and set Error::UnsupportedFeature on PCA9555.

Method	Signature	Location
`EnableInputLatch()`	`bool EnableInputLatch(uint16_t pin, bool enable)`	`src/pcal95555.ipp`
`EnableInputLatches()`	`bool EnableInputLatches(std::initializer_list<std::pair<uint16_t, bool>> configs)`	`src/pcal95555.ipp`
`EnableMultipleInputLatches()`	`bool EnableMultipleInputLatches(uint16_t mask, bool enable)`	`src/pcal95555.ipp`

Address Management

Method	Signature	Location
`GetAddress()`	`uint8_t GetAddress() const`	`src/pcal95555.ipp`
`GetAddressBits()`	`uint8_t GetAddressBits() const`	`src/pcal95555.ipp`
`ChangeAddress()`	`bool ChangeAddress(bool a0_level, bool a1_level, bool a2_level)`	`src/pcal95555.ipp`
`ChangeAddress()`	`bool ChangeAddress(uint8_t address)`	`src/pcal95555.ipp`

Error Handling

Method	Signature	Location
`SetRetries()`	`void SetRetries(int retries) noexcept`	`src/pcal95555.ipp`
`GetErrorFlags()`	`[[nodiscard]] uint16_t GetErrorFlags() const noexcept`	`src/pcal95555.ipp`
`ClearErrorFlags()`	`void ClearErrorFlags(uint16_t mask = 0xFFFF) noexcept`	`src/pcal95555.ipp`

Chip Variant Detection

Method	Signature	Description	Location
`HasAgileIO()`	`[[nodiscard]] bool HasAgileIO() const noexcept`	Returns `true` if PCAL9555A detected (Agile I/O available)	`src/pcal95555.ipp`
`GetChipVariant()`	`[[nodiscard]] ChipVariant GetChipVariant() const noexcept`	Returns the detected `ChipVariant` enum value	`src/pcal95555.ipp`

Usage:

if (driver.HasAgileIO()) {
    // PCAL9555A features available
    driver.SetDriveStrength(0, DriveStrength::Level2);
} else {
    // PCA9555 -- only standard registers
}
 
auto variant = driver.GetChipVariant();
// ChipVariant::Unknown, ChipVariant::PCA9555, or ChipVariant::PCAL9555A

Types

Enumerations

Type	Values	Description	Location
`GPIODir`	`Input`, `Output`	GPIO pin direction	`inc/pcal95555.hpp`
`DriveStrength`	`Level0`, `Level1`, `Level2`, `Level3`	Output drive strength (Level0=25%, Level1=50%, Level2=75%, Level3=100%). PCAL9555A only.	`inc/pcal95555.hpp`
`Polarity`	`Normal`, `Inverted`	Input polarity inversion	`inc/pcal95555.hpp`
`OutputMode`	`PushPull`, `OpenDrain`	Output mode (per port). PCAL9555A only.	`inc/pcal95555.hpp`
`InterruptState`	`Enabled`, `Disabled`	Interrupt enable/disable state. PCAL9555A only.	`inc/pcal95555.hpp`
`InterruptEdge`	`Rising`, `Falling`, `Both`	Interrupt edge trigger type (works on both variants via software)	`inc/pcal95555.hpp`
`ChipVariant`	`Unknown`, `PCA9555`, `PCAL9555A`	Detected or user-specified chip variant	`inc/pcal95555.hpp`
`Error`	`None`, `InvalidPin`, `InvalidMask`, `I2CReadFail`, `I2CWriteFail`, `UnsupportedFeature`, `InvalidAddress`	Error conditions (bitmask). `UnsupportedFeature` (0x0010) is set when a PCAL9555A-only method is called on a PCA9555. `InvalidAddress` (0x0020) is set when an I2C address outside the valid 0x20-0x27 range is provided.	`inc/pcal95555.hpp`