[Coco] [Color Computer] Hardware specifics regarding GIME , RAM and ROM

[news at wzydhek.com]

One other question.. How does the overlaying of ROMs work? Is Super Extended
Basic a 32k ROM or A 16k ROM? I have seen data indicating that it is a full
32k, but that the DISK ROM overwrite or shadows the later 16k?
 
-Walt Zydhek

  _____  

From: ColorComputer at yahoogroups.com [mailto:ColorComputer at yahoogroups.com]
On Behalf Of news at wzydhek.com
Sent: Wednesday, April 29, 2009 8:36 PM
To: ColorComputer at yahoogroups.com
Subject: [Color Computer] Hardware specifics regarding GIME , RAM and ROM




I have a few questions regarding the GIME, RAM and ROM.
 
1) If I understant what I have read so far, if $FFDE is written to, then the
memory will be in ROM mode, meaning $8000-$FEFF will be accessed from rom?
How does the MMU registers $FFA0-$FFAF affect this? Can those ROM addresses
be remapped to different memory slots? (Instead of $8000 being at $78000,
can it be read from the equivalent of $18000, etc?)
 
2) When $FFDF is written to set RAM mode, are the ROMs no longer accessible
until $FFDE is written back to?
 
3) Also, if I understand correctly, there is 32K worth of ROM space, mapped
either 32K internal, 32K internal (Cartridge?), or 16K internal/16K
external. Does bit 2 (MC2) of $FF90 determine WHICH external ROM (if there
is a multipack in use) is mapped for the 32k external or 16k external?
 
4) Is $FF00 - FFEF ALWAYS mapped for hardware no matter what MMU registers
are set or RAM/ROM mode, etc? And are they always mapped to $7FF00 - $7FFEF?
And what about $FFF0-$FFFF, I understand they are mapped to $BFF0-$BFFF for
the vectors in the ROM. Is this ALWAYS the case no matter what the MMU
registers and RAM/ROM mode are set for?
 
5) Lastly, I guess bit 3 of $FF90 controls whether the 256 bytes from
$FE00-FEFF are always present at that address no matter if banks are
switched around? If so, is this space mapped to $7FE00 to $7FEFF?
 
I am trying to get a better understanding of how the GIME, RAM and ROM
interract.
 
-Walt Zydhek