Bit 0 behavior, take 2

[Lucas <lscharen@gmail.com>]

For some reason my previous post got screwed up going through Google
Groups.  Trying again....

I was wondering if anyone could clearly explain the behavior of bit 0
in the New Video Register ($C029).  The IIgs Technical Reference's
explanation is very unclear (quoted, page 90) and I think they
reversed the meaning of 0 and 1 in the docs, since the SHR screen is
usually enabled by writing $C1 to $C029.

"""
Enable bank latch.  If this bit if 1, the 17th address bit is used to
select either the main or auxiliary memory bank.  If the address bit
is 1, then the auxiliary bank is enabled. (Actually data bit 0 is used
as the 17th address bit).  If the address bit is 0, the state of the
memory configuration soft switches determines which memory bank is
enabled.
"""

I *assume* that they mean the first bit of the Data Bank register is
used to select between Bank 0 and Bank 1, which means that one can
shadow to the SHR screen from any bank in memory.  I thought I had
heard the MegaDemo used a trick involving this bit, too.

My real GS is not handily available for testing and I don't
necessarily trust the accuracy of the emulators on a subtle point like
this.

Comments?

-Lucas