Hello Chris,
> Can anyone point me to where I can find information on the SARA chip?
>
> For cartridges that carry RAM, can someone point me to where I can find
> information on how the Atari writes to RAM on a cartridge?
>From a programmers point of view the SARA RAM is quite simple.
There are 128 bytes of RAM. You can write to it normally at
addresses $F000-$F07F. Reading from addresses $F080-$F0FF will
get the data from the same 128 bytes of RAM. Just remember that
all accesses at $F000-$F07F will be treated as write accesses.
So don't read from these addresses, or you will corrupt the
contents of the RAM.
> Can someone help me better understand ParkerBrothers E0 bankswitching?
The
> current description is confusing me. I don't fully understand the
> difference between Segments and Slices...
Segments describes _WHERE_ the data can be accessed, and
slices describes _WHAT_ part of the ROM you can access there.
The 8K game ROM is seperated into 8 1K parts (slices). Each
of these slices can be mapped into the 2600 memory at 4
different positions (segments). The four segments are:
$F000-$F3FF
$F400-$F7FF
$F800-$FBFF
$FC00-$FFFF
Each of the 8 ROM slices (0-7) can be mapped into the first
three memory segments. The last slice (7) is always mapped into
the last memory segment ($FC00-$FFFF). The select which ROM slice
goes into which memory segment there are three hotspot areas:
$FFE0-$FFE7 (for the first segment)
$FFE8-$FFEF (for the second segment)
$FFF0-$FFF7 (for the third segment)
So if you do "LDA $FFE0" it will mean that you can access the
first 1K of your game ROM at addresses $F000-$F3FF. And if
you do "LDA $FFEF" it means that you can access the last
1K of your game ROM at addresses $F400-$F7FF.
Ciao, Eckhard Stolberg
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