Audio Cpu Memory Map

Visual Summary

	.00000	.40000	.80000	.C0000
0.....	Work Ram / Program Rom**
1.....		Dual-Port Ram
2.....	Otis Registers	Esp Registers		Duart Registers
3.....	Otis Voices' Banks	Volume Registers
4.....
5.....
6.....
7.....
8.....
9.....
A.....
B.....
C.....	Program Rom* (maximum size?)
D.....
E.....
F.....			Work Ram

The actual (non-mirrored) size of each region is shown in green, if visible. (very small regions are indicated by a triangle in the corner).

Address Map

Name	Address Bits	Address Spaces	Width	Start
Program Rom**	[0000 0?aa aaaa aaaa aaaa aaaA]*	supervisor program*	16-bit	$000000
Program Rom	[1100 0?aa aaaa aaaa aaaa aaaA]*	data, program*	16-bit	$C00000
Work Ram	[0000 0... aaaa aaaa aaaa aaaA] [1111 1... aaaa aaaa aaaa aaaA]	data, user program?	16-bit	$000000
Dual-Port Ram	[0001 01.. .... aaaa aaaa aaa0]	data/?	8-bit (even)	$140000
Otis Registers	[0010 00.. .... .... ...a aaaA]	data/?	16-bit	$200000
Esp Registers	[0010 01.. .... ...a aaaa aaa1]	data/?	8-bit (odd)	$240000
Duart Registers	[0010 10.. .... .... ...a aaa1]	data/?	8-bit (odd)	$280000
Otis Voices' Banks	[0011 00.. .... .... ..aa aaa1]	data/?	8-bit (odd)	$300000
Volume Registers	[0011 01.. .... .... .... ..a0]	data/?	8-bit (even)	$340000

*The size and mapping of program rom depends on the cartridge.

**In supervisor program space, the program roms, instead of ram, are available at address 0 (in addition to their normal location). (This was done to allow reading the pc reset vector at startup).

address bits legend:

0/1: mapping bit (must match)
.: doesn't matter
a: "real" address bit
A: address bit that just selects a byte within the data bus

Notes

Accessing unmapped addresses will freeze the cpu, not trigger a bus error.

Ram is mirrored to the top of address space because they wanted all of it to be accessable via signed 16-bit offsets from $0.