Motorola 68040 (MC68040) is the next generation of
68020 / 68030
32-bit microprocessors. The CPU has 32-bit address and data buses,
and can address up to 4 GB of memory. The 68040 has two privilege
modes - user mode and supervisor mode. User mode is object-code
compatible with earlier generations of 680x0 processors. Supervisor
mode is not fully compatible with earlier 68K CPUs due to changes in
memory management and exception processing. The 68040 supports new
synchronous and burst bus modes, that were introduced by 68030 CPU.
The processor includes a few enhancements that improve processor
performance. The size of each cache on the 68040 CPU was increased to
4 KB. The CPU also integrates Floating Point Unit. The integrated FPU
can execute most common Motorola 68881 /
68882 instructions and data types.
Execution time of all supported Floating-Point instructions was
significantly reduced. All unsupported FP instructions and data types
are emulated in software. The Motorola 68040 also features separate
memory management units for instructions and data, and multiple
independent execution pipelines. Some internal logic of the Motorola
68040 uses 2x clock frequency, but the processor cannot be considered
double-clocked.
In addition to basic MC68040 version, that included both FPU and MMU
units, the following modifications were produced:
- 68LC040 (MC68LC040) does not include FPU.
- 68EC040 (MC68EC040) does not include FPU and MMU units
- 68040V (MC68040V) is a 3.3V static processor that can be clocked
down to 0 MHz. This CPU doesn't include integrated FPU.
- 68EC040V (MC68EC040V) - is a 3.3V static processor without FPU and
MMU units.
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