Motorola 68020 (MC68020) is a 32-bit microprocessor compatible with
earlier members of 680x0 family - 68000,
68008 and
68010. Address bus width on the 68020
is increased to 32 bits, which allows the processor to address up to
4 GB of memory. Data bus width is also increased to 32 bits, though
if necessary the 68020 can work with 8- and 16-bit data buses.
Other Motorola 68020 enhancements include:
- Execution time of many instructions was reduced.
- To improve CPU performance, a 256-byte instruction cache was added
to the CPU.
- The CPU includes new control registers.
- The CPU has new addressing modes: memory indirect addressing modes,
scaled index, and larger displacements.
- New instructions were added to 68020 instruction set: bit field
instructions, compare instructions, call module and pack/unpack BCD.
- The MC68020 provides hardware support for
Motorola 68881 and
68882 Floating-Point Units.
- Accessing mis-aligned word or long-word data no longer results in a
system error, though access to misaligned data is not as fast as
access to properly aligned data.
Motorola also manufactured MC68EC020 - embedded version of the
MC68020 CPU. The 68EC020 had only 24-bit address bus, and could
address up to 16 MB of physical memory. The MC68EC020 was
housed in different packages than the Motorola 68020 microprocessor.
Some Motorola 68020 and 68EC020 microprocessors were marked with custom
part numbers. To identify these processors please see
List of Motorola custom part numbers.
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