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Hardware:Memory Map

From Motorola 68000 Homebrew Computer Project

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Memory Map

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

0MB: 0x00000000 - 0x001FFFFF ROM 2 MB
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