Hardware:Memory Map

Memory Map

The 16MB of address space will be broken up into 8 2MB chunks by a 74LS138 3-to-8 decoder.

0MB: 0x00000000 - 0x000FFFFF ROM 1 MB
1MB: 0x00100000 - 0x001FFFFF Reserved 1 MB, possible future use for more memory mapped I/O or VRAM, etc.
2MB: 0x00200000 - 0x003FFFFF Memory Mapped I/O 2 MB
4MB: 0x00400000 - 0x00FFFFFF Static RAM 12 MB

Memory mapped I/O area from 0x00200000 - 0x003FFFFF will be broken down with another 74LS138 into 8 256KB chunks or maybe with a 74LS154 4-to-16 decoder for 16 chunks. I still haven't decided 100% yet.

Device Address Map (74LS138)

8 chunks of 256KB

Device Number	Address Range	Description
0	0x00200000 - 0x0023FFFF	68901 Multi-Function Peripheral (MFP)
1	0x00240000 - 0x0027FFFF	Future I/O Device
2	0x00280000 - 0x002BFFFF	Future I/O Device
3	0x002C0000 - 0x002FFFFF	Future I/O Device
4	0x00300000 - 0x0033FFFF	Future I/O Device
5	0x00340000 - 0x0037FFFF	Future I/O Device
6	0x00380000 - 0x003BFFFF	Future I/O Device
7	0x003C0000 - 0x003FFFFF	Future I/O Device

Device Address Map (74LS154)

16 chunks of 128KB

Device Number	Address Range	Description
0	0x00200000 - 0x0021FFFF	68901 Multi-Function Peripheral (MFP)
1	0x00220000 - 0x0023FFFF	Future I/O Device
2	0x00240000 - 0x0025FFFF	Future I/O Device
3	0x00260000 - 0x0027FFFF	Future I/O Device
4	0x00280000 - 0x0029FFFF	Future I/O Device
5	0x002A0000 - 0x002BFFFF	Future I/O Device
6	0x002C0000 - 0x002DFFFF	Future I/O Device
7	0x002E0000 - 0x002FFFFF	Future I/O Device
8	0x00300000 - 0x0031FFFF	Future I/O Device
9	0x00320000 - 0x0033FFFF	Future I/O Device
10	0x00340000 - 0x0035FFFF	Future I/O Device
11	0x00360000 - 0x0037FFFF	Future I/O Device
12	0x00380000 - 0x0039FFFF	Future I/O Device
13	0x003A0000 - 0x003BFFFF	Future I/O Device
14	0x003C0000 - 0x003DFFFF	Future I/O Device
15	0x003E0000 - 0x003FFFFF	Future I/O Device