Raspberry Pi i2c GPIO Expander MCP23017

So, you've got a raspberry pi and want more GPIO? Grab one of these expander hats.

This document will walk you through command line use of outputs.

CLI

The main program we will use is i2cset.

Arguments You Need

1. -y disables interactive mode
2. 1 (the default i2c bus on the pi)
3. 0x23 IO chip address (set by 3 bit switches)
4. 0x00 8 bit data address
5. 0x00 8 bit data values

How To Use Outputs

1. Set pin modes to output:
   • set all A pins as outputs i2cset -y 1 0x23 0x00 0x00 (all outputs)
   • set all B pins as outputs i2cset -y 1 0x23 0x01 0x00 (all outputs)
2. Send a command
   • set all A bank pins on i2cset -y 1 0x23 0x14 0xFF
   • set all A bank pins off i2cset -y 1 0x23 0x14 0x00
   • set all B bank pins on i2cset -y 1 0x23 0x15 0xFF
   • set all B bank pins off i2cset -y 1 0x23 0x15 0x00

Individual Pins

Pin Label	Register	Hex Value
A0	0x014	0x01
A1	0x014	0x02
A2	0x014	0x04
A3	0x014	0x08
A4	0x014	0x10
A5	0x014	0x20
A6	0x014	0x40
A7	0x014	0x80
B0	0x015	0x01
B1	0x015	0x02
B2	0x015	0x04
B3	0x015	0x08
B4	0x015	0x10
B5	0x015	0x20
B6	0x015	0x40
B7	0x015	0x80

How To Use Inputs

1. Set pin modes to input:
   • set A register i2cset -y 1 0x23 0x00 0xFF (all inputs)
   • set B register i2cset -y 1 0x23 0x01 0xFF (all inputs)

Resources

• MCP23017 Datasheet
• Raspberry Pi HAT - 32 I/O Port Expander
• Interfacing an I2C GPIO expander (MCP23017) to the Raspberry Pi using C++ (i2cdev)