CODE EXAMPLE FOR SHELL

set pin on mcp23017 using raspberry pi shell

# for original rev1 Pi
sudo i2cset -y 0 0x20 0x00 0xff
sudo i2cset -y 0 0x20 0x14 0x01
#           address register value 
# for rev2 Pi or later
sudo i2cset -y 1 0x20 0x00 0xff
sudo i2cset -y 1 0x20 0x14 0x01
#           address register value