What do I need A0 in a USB Controller (PDIUSBD12)?
When used with non-multiplexed data/address buses, the A0 pin determines whether the byte is command or data. The rest of the address lines from the MPU/MCU should be decoded to enable CS_N appropriately for selecting the device.

When used with multiplexed data/address buses, the A0 pin is ignored and instead the multiplexed A0 (on D0 when the address is being latched, i.e. when ALE falls) is used to determine the mode. The other 7 address bits are ignored, and should be decoded for CS_N as normal.