How to connect and wire multiple mcp23017 port ex panders

Thread Starter


Joined Jan 27, 2009
I need to connect these expanders to a Teensy 3.6 board to give me 48 more digital pins. I was told to do it this way but how would board identify mcp 1,2, or 3?mcp 2.jpg
Last edited:


Joined Feb 20, 2016
You need to have A0, A1 and A2 wired differently for each chip. That is the address selection.
Connect to Vss or Vdd in a binary number fashion.


Joined Feb 20, 2016
First one, A0, A1 and A2 to Vss. = "0"
Second one , A0 to Vdd, A1 and A2 to Vss. = "1"
Third, A0 and A2 to Vss, A1 to Vdd = "2"
Fourth, A0 and A1 to Vdd, A2 to Vss. = "3"
And so on.
Look up binary numbers.

MCP23017 Address.jpg