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MCP23017 IO Expansion Board, I2C Interface, Expands 16 I/O Pins

  • 16 GPIOs split into Port A (GPA0–GPA7) and Port B (GPB0–GPB7)
  • Per-pin direction control (input or output)
  • Internal pull-ups for inputs (ideal for buttons/switches)
  • Interrupt support via INTA/INTB pins (or mirrored)
  • Up to 8 devices on one I²C bus (addresses via A0–A2)
  • Operates at 3.3V or 5V (logic follows VDD)

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Address

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Connector

# name Color (PH2.0 20cm 6Pin x1)
1 vcc red
2 gnd black
3 SDA blue
4 SCL yellow
5 INTA orange
6 INTB green

CP2112

The CP2112 USB-to-I2C Bridge is a communication device between a USB host (like a PC) and I2C devices

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install

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sudo apt install i2c-tools

usage

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i2cdetect -l
#
i2c-0   unknown     Synopsys DesignWare I2C adapter     N/A
i2c-1   unknown     Synopsys DesignWare I2C adapter     N/A
..
i2c-21  unknown     CP2112 SMBus Bridge on hidraw6      N/A

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sudo i2cdetect -y -r 21
#
     0  1  2  3  4  5  6  7  8  9  a  b  c  d  e  f
00:                         -- -- -- -- -- -- -- -- 
10: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- 
20: -- -- -- -- -- -- -- 27 -- -- -- -- -- -- -- -- 
30: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- 
40: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- 
50: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- 
60: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- --

Output

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Register Use for Read gives
IODIRA Direction 1=input, 0=output
GPPUA Pull-ups Enabled bits
OLATA Output latch Last written output values
GPIOA Pin state Actual pin logic level
INTCAPA Interrupt snapshot Pin state at interrupt

OLATA vs GPIOA

  • To CONTROL pins → OLATA
  • To OBSERVE pins → GPIOA

i2c-tools

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sudo apt install i2c-tools
i2cset cli
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i2cset [OPTIONS] BUS SLAVE_ADDR REGISTER VALUE [MODE]

1️⃣ IODIRA(0x00) — I/O Direction Register (Port A) IODIRA controls whether each Port A pin is an input or output.

  • Address: 0x00
  • Reset value: 0xFF (all inputs)
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Bit = 1 → INPUT  (output driver OFF, Hi-Z)
Bit = 0 → OUTPUT (output driver ON)
Demo
  • Config GPA0 as output 0xFE using IODIRA register
  • Set/ Unset output value using register OLATA register
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# i2cset [OPTIONS] BUS SLAVE_ADDR REGISTER VALUE [MODE]
sudo i2cset -y 21 0x27 0x00 0xFE b
sudo i2cset -y 21 0x27 0x14 0x01 b
sudo i2cset -y 21 0x27 0x14 0x00 b

Input

Demo:

  • Config GPA1 as input
  • Config it as pull-up: GPA1 ----[ button ]---- GND
  • Create poll loop

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init
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# config GPA1 as input
#bus: 21 address:0x27 IODIRA: 0x00 GPIA1: bit (1) 0x02
i2cset -y 21 0x27 0x00 0x02 b

# config GPA1 as pull up
# GPPUA register: 0x0c
i2cset -y 21 0x27 0x0C 0x02 b
poll_loop.sh
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#/bin/bash
i2cset -y 21 0x27 0x00 0x02
i2cset -y 21 0x27 0x0C 0x02

last=""

while true; do
  v=$(i2cget -y 21 0x27 0x12)
  # convert hex string (0x..) to number
  n=$((v))

  if [ $((n & 0x02)) -eq 0 ]; then
    s="pressed"
  else
    s="released"
  fi

  if [ "$s" != "$last" ]; then
    echo "$s ($v)"
    last="$s"
  fi

  sleep 0.05
done

TODO: implement INT on rpi and jetson board

Python

blink LED
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from smbus2 import SMBus
import time


ADDRESS = 0x27
BUS = 21
REG_IODIRA = 0x00
REG_OLATA = 0x14
GPA0 = 0x01

# Initialize SMBus
bus = SMBus(BUS)
# Set GPA0 as output
iodir = bus.read_byte_data(ADDRESS, REG_IODIRA)
iodir &= ~GPA0
bus.write_byte_data(ADDRESS, REG_IODIRA, iodir)

while True:
    # Read current OLATA value
    olata = bus.read_byte_data(ADDRESS, REG_IODIRA)
    # Set GPA0 high
    olata |= GPA0
    # Write OLATA with GPA0 high
    bus.write_byte_data(ADDRESS, REG_OLATA, olata)  # OLATA
    time.sleep(1)
    olata = bus.read_byte_data(ADDRESS, REG_IODIRA)
    # Set GPA0 low
    olata &= ~GPA0
    # Write OLATA with GPA0 low
    bus.write_byte_data(ADDRESS, REG_OLATA, olata)  # OLATA
    time.sleep(1)

TODO

  • implement interrupt using rpi
  • implement python simple pool

Reference