13 The MCP23017 and MCP23008 GPIO Expanders
Most SBCs and MCUs provide anywhere from three to a couple dozen digital I/O pins. Sometimes, you’ll need more digital I/O than the standard complement. Even on those MCUs that provide a couple dozen pins or more, most of them are multifunction. If you use them for their alternate purposes, you may find that you don’t have enough remaining pins for digital I/O. This is where a GPIO expander comes in handy.
While there are many different ICs you can purchase to provide GPIO expansion on the I2C bus, the MCP23008 and MCP23017 (collectively MCP230xx) are popular; they’re available in DIP (through-hole) ...
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