The bus is just a bunch of wires. It has no active logic. When not driven, weak pulldowns keep the levels at zero.

This example is 51 bits wide: 32 data bits + 16 instruction word bits + 3 control signals (copy start, copy in progress, and copy done).

We can have other data and instruction word widths. If the number of registers in a WIZ is less than 128 we could have 7-bit register addresses and a 14-bit instruction word. A viable WIZ can be constructed with just 8 registers and a 3-bit register address and a 6-bit instruction word. Indeed, these minimal WIZes will be common! (More on that later).

And finally, no matter the widths of the other parts, there are always the same three control signals.