johnwasser:
Nine equal resistors would work. Each tap would be a different voltage. Note that 0V and Vcc are not among the 8 voltages you can choose from. That's why you use 9 resistors.
No, 7 resistors and 0V and Vcc are among the valid 8 voltages. Fig 1-3 in datasheet. Unless you want to run more than one IO expander just wire ADDR pin to ground.