Nice Z80+ Operation Manual page 71

To overlay ROM area-opera ting from overlay RAM
>
EOR 2911
> "
llBl,IFFF,2111
>
EOR 11111
>
STS
--->
nll II D
--->IHI II D
--->
11111 Ill D
IBR
Overlay RA" is enabled it llll-1FFF R/W
>
6 I
66.
Overlay RAM enabled, base address does not
overlap area where ROM code resides.
Move contents of ROM to overlay RAM
Emulator RAM overlays system ROM.
The GO command is issued and operation
commences from emulator overlay RAM.
In this example, overlay RAM is defined as R/W
because the target system RAM starts at 1800 H
and the overlay crosses the system RAM/ROM
boundary.