<p><pre><code>    add ix iy
</code></pre>
I&#x27;m pretty sure that isn&#x27;t a thing (the z80 has prefix opcodes for &quot;hl in next instruction is really ix (or (hl) is (ix+dd)&quot; and one for iy, but not one for both in the same instruction like that). Source: worked on a product with a z80 in this decade.