[Coco] Bringing ext. ROM back into active memory map?

[Bruce Borer]

Hi All,
    I am new to programming the CoCo (after 40 years).
    My question for today is: On a CoCo3 which copies everything to
RAM how do I bring back the actual ROM back into the active memory
map?
Just "POKE &Hff90,&H0C" does not work.
    I have a board with the ROM replaced with Flash and it is able to
be programmed in circuit if CTS is made active again.  I prefer not to
make a separate board just to program the Flash then insert the
programmed Flash into my cartridge.
    If I get this working I plan to release my design to the community.

Bruce P. Borer