from Kevtris' pages:
http://www.tripoint.org/kevtris/mappers ... R1ROM.html
http://www.tripoint.org/kevtris/mappers ... TVROM.html
I'm trying to understand the specifics. What I know:
- These boards have only 4k usable RAM (presumably accessed via $6000-$6FFF).
- $7xxx mirrors $6xxx (A12 pulled low)
- despite only 4k of RAM being accessable, 8k of RAM exists on the board
What I am unsure about:
- I know at least the two extra nametables for the 4-screen mirroring come from cartridge RAM. But do all 4 nametables use cartridge RAM (leaving the PPUs internal nametables unused)?
- It makes sense that the nametables would exist on the unused area of RAM ($7800-$7FFF -- or $7000-$7FFF if all 4 nametables). But is that the case? Or do they exist at the same RAM accessed via $6xxx?
- If the above is the case, would it be possible to draw to the nametables by writing to $6xxx?
Anyway, any light shed on the situation would be appreciated ^^. I know this stuff isn't necessary for emulating Gauntlet and Rad Racer 2, but I'd like to know anyway. Thanks in advance.
http://www.tripoint.org/kevtris/mappers ... R1ROM.html
http://www.tripoint.org/kevtris/mappers ... TVROM.html
I'm trying to understand the specifics. What I know:
- These boards have only 4k usable RAM (presumably accessed via $6000-$6FFF).
- $7xxx mirrors $6xxx (A12 pulled low)
- despite only 4k of RAM being accessable, 8k of RAM exists on the board
What I am unsure about:
- I know at least the two extra nametables for the 4-screen mirroring come from cartridge RAM. But do all 4 nametables use cartridge RAM (leaving the PPUs internal nametables unused)?
- It makes sense that the nametables would exist on the unused area of RAM ($7800-$7FFF -- or $7000-$7FFF if all 4 nametables). But is that the case? Or do they exist at the same RAM accessed via $6xxx?
- If the above is the case, would it be possible to draw to the nametables by writing to $6xxx?
Anyway, any light shed on the situation would be appreciated ^^. I know this stuff isn't necessary for emulating Gauntlet and Rad Racer 2, but I'd like to know anyway. Thanks in advance.