Memory Map of MB020

MB020 uses 256 megabyte of 68020's 4 gigabyte memory space. The I/O is 8-bit wide bus located at top of memory; the boot space is 0x0-0x3FFFFFF 8-bit wide data bus mapped to RC2014 expansion bus; the main memory is from 0x4000000-0xBFFFFFF.

Boot Memory

Boot memory is mapped to RC2014 expansion bus. It is 8-bit wide, 1 wait state access. RC2014 8K ROM board or 512K RAM/ROM board can serve as the boot memory.

Boot Memory: 0x0-0x3FFFFFF

Main Memory

Main memory is a 72-pin SIMM board located on MB020. It is 32-bit wide, zero wait state memory. The SIMM memory may be 4meg, 8meg, 16meg, or 32 meg 60ns EDO or FP memory with no parity. The refresh logic in CPLD automatically refresh the SIMM memory.

Main Memory: 4000000-BFFFFFF

I/O Space

I/O is 8-bit wide data bus located at top of the memory. I/O access has 4 wait states. I/O access causes nIORQ signal on RC2014 bus to be asserted along with address lines A0-A11.

I/O Space: 0xFFFFF000-0xFFFFFFFF

Swap Register

Swap register is located in 0xFFFF8000 such that any access to it (read or write) swap the lowest 64 meg memory with next 64 meg memory, i.e., boot memory located in 0x0-0x3FFFFFF is now located at 0x4000000-0x7FFFFFF and main memory that was located in 0x4000000-0x7FFFFFF is now located at 0x0-0x3FFFFFF. Swapping can not be undone, except by reset.

builderpages/plasmo/mb020/mem_map.txt · Last modified: 2020/02/15 20:06 by plasmo
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