I have spent countless days trying to get this thing to work. For anyone that has gotten it to work, what libraries are you using? I found two MCP23S1.h libraries. One is by dreamcat4 and the other by Cort Buffington. The dreamcat4 one is old and requires an outdated Spi.h library which cannot be found on the internet. Mr. Buffington's is newer, but just flat out does not work for me. There is literally nothing on the internet on how to get these dang things to work. All I want to do it light up one led, how hard can this be? I tied A0-A2 to ground so my address is 000, I tied reset to 5V, and the serial pins to the respective ones on the Arduino. It has 16 I/O pins and all I want to do is light up one led! I have never gotten this chip to work since I bought it, I've used shift registers but not these guys. It would also be really helpful to see someone's code on how to light up just one led with this chip and what library you are using. Any help would be deeply appreciated!