MCP23017 I/O Expander Help

i'm trying learn mcp23017 i/o expander using uno board.

i'm following tutorial here: http://www.learningaboutelectronics.com/articles/mcp23017-io-port-expander-circuit-with-arduino.php

there statement: "and connect address pins, pins a0, a1, , a2, ground. makes address of these 3 pins 000".

i understand concept of using these 3 pins chain more expanders , how binary value determines expander board active board, etc. in example connecting leds these 3 ports.

how can connect these ports ground , use them controlling leds? seems me can't both @ same time?

thanks..

you're getting a0~a2 (the address pins, physical pins 15-17) confused gpa0~gpa2 (the first 3 i/o pins of mcp23017's port a, physical pins 21~23)

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