Motorola 68040 (MC68040) microprocessor family

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.