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This is a library for the MCP23008/17 I2C and MCP23S08/17 SPI Port Expanders.

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Written by Carter Nelson for Adafruit Industries.BSD license, check license.txt for more informationAll text above must be included in any redistribution

To install, use the Arduino IDE Library Manager.

When using single pin operations such aspinMode(pinId, dir) ordigitalRead(pinId) ordigitalWrite(pinId, val) then the pins are addressed using the ID's below. For example, for set the mode ofGPB0 then usepinMode(8, ...).NOTE The MCP23008 and MCP23S08 only haveGPAx pins.

Library supports MCP23Sxx HW pin addressing (A2, A1, A0 for S17 and A1, A0 for S08)To use it provide HW address to begin_SPI(CS, SPI, HW_ADDR) function, and as a result each SPI message will contain correct chip address.

Example:mcp.begin_SPI(10, &SPI, 0b101);

HW Address recognition must be enabled by enableAddrPins() function.NOTE Calling enableAddrPins() will enable IOCON.HAEN bit for all active (CS low) devices on SPI bus.NOTEThere is hardware bug in the MCP23S17 chip, see "MCP23S17 Rev. A Silicon Errata".As a result, if using device with A2 = high, and not using addressing, hw address must be set to 0b1XXIn such case, even if not using addressing, initalize your MCP23S17 chip with 0b1XX address, eg: mcp.begin_SPI(10, &SPI, 0b100);.

Some people have reported an undocumented bug that can potentially corrupt the I2C bus.It occurs if an MCP230XX input pin state changes during I2C readout.This should be very rare. For more information, see thisforum post and thisknowledge base article.