Konami Sound Cartridge - Using The Memory

Using The Memory

Everything is done using memory-mapped I/O and it is much like the SCC ROM cartridges.

As with SCC cartridges, the memory is divided into four memory banks of 8kB:

Bank 1

4000h - 5FFFh

Bank 2

6000h - 7FFFh

Bank 3

8000h - 9FFFh

Bank 4

A000h - BFFFh

To change the mapping, write to one of these addresses:

Bank 1

5000h - 57FFh

Bank 2

7000h - 77FFh

Bank 3

9000h - 97FFh

Bank 4

B000h - B7FFh

Bits 3 through 7 are ignored. Values 0 to 7 select 8kB pages of the lower 64kB (which is included with Snatcher) and values 8 to 15 the higher 64kB (which is included with SD Snatcher).

By default (after reset) bank 1 selected area 0, bank 2 area 1, bank 3 area 2 and bank 4 area 3. Again this is the same as SCC ROM cartridges. If the lower 64kB is empty (as it is with the Super Deform Snatcher cartridge) then the memory will be empty (reads FFh).

By default, the RAM cannot be changed. By setting a bit somewhere else the areas can no longer be changed (ROM mode) but can be written to (RAM mode). This is done by writing to the mode register, which is always accessible through address BFFEh and BFFFh. The SCC can be put in also be put in SCC+ mode through this register, where channel 4 and 5 do not share a waveform.

bit 7

no function

bit 6

no function

bit 5

if set, sound chip is in SCC+ mode otherwise SCC compatibility

bit 4

if set, banks 1 to 3 are in RAM mode otherwise area select

bit 3

no function

bit 2

if set and bit 5 reset, bank 3 is RAM mode irrespective of bit 4

bit 1

if set, bank 2 is RAM mode irrespective of bit 4

bit 0

if set, bank 1 is RAM mode irrespective of bit 4

Even in RAM mode the memory under BFFEh and BFFFh cannot be changed through those addresses as that will always end up in the mode register.

Konami uses 20h and 3Fh for the mode register as they always use SCC+ mode. 30h would also work for RAM mode.