Prefixed instruction has only one M1 ?
IO_ACK is itself a separated instruction, 4T. So IO_ACK offset into INT (interrupt) should not implicated by WAIT_n generator, and it seems that a WAIT_n during T2 is ignored because of autowait already inserted at this moment... for synchronizing an IO_ACK, I have normaly to insert WAIT_n during heu.
=== Test of a real Zilog 80 ===