mcp23017 v0.1.0

MCP23017 16-bit I2C GPIO expander.

Application scenarios

• Extra buttons, relays, or LEDs on a small MCU.
• A keypad or DIP switch bank.
• Isolating a slow control panel from the main board.

Contract

uint8_t mcp23017_init(mcp23017_t *device, mcp23017_port_t port, uint8_t i2c_address);
uint8_t mcp23017_pin_mode(mcp23017_t *device, uint8_t pin, uint8_t output);
uint8_t mcp23017_write_pin(mcp23017_t *device, uint8_t pin, uint8_t value);
uint8_t mcp23017_read_pin(mcp23017_t *device, uint8_t pin, uint8_t *value);
uint8_t mcp23017_write_port(mcp23017_t *device, uint8_t port, uint8_t value);
uint8_t mcp23017_read_port(mcp23017_t *device, uint8_t port, uint8_t *value);
uint8_t mcp23017_set_pullup(mcp23017_t *device, uint8_t pin, uint8_t enable);

• Pins 0..7 are port A; pins 8..15 are port B.
• init uses IOCON.BANK=0 and sets all pins as inputs with pull-ups off.
• write_pin changes one output latch bit; other bits keep their state.
• Returns 1 on success, 0 on a bad pin or a bus error.

Parameters

• I2C address 0x20..0x27 from A2/A1/A0.
• pin_mode 0 = input, 1 = output.
• Pull-ups are useful for buttons; disable them for driven inputs.

Memory and timing

• 4 bytes; one or two I2C transactions per call.
• A 400 kHz bus updates a pin in about 60 us.

Integration

mcp23017_t expander;
mcp23017_init(&expander, board_i2c_port(), 0x20);
mcp23017_pin_mode(&expander, 0, 1);
mcp23017_write_pin(&expander, 0, 1);

Adapters

• The adapter issues a register write followed by a repeated-start read.
• Reference: blemasle/arduino-mcp23017 (MIT) and the Microchip MCP23017 datasheet.
• This implementation is original.

When not to use

• A pin that needs a hardware timer, ADC, or interrupt latency; use the MCU.
• More than 16 pins; use multiple expanders.

Verification

make test covers init, pin direction, output latch updates, input reads,

ports, and pull-ups.

void *context;
uint8_t (*write)(void *context, uint8_t address, uint8_t reg,
const uint8_t *data, uint16_t length);
uint8_t (*read)(void *context, uint8_t address, uint8_t reg,
uint8_t *data, uint16_t length);

mcp23017_port_t port;
uint8_t i2c_address;