MC68030 Datasheet, PDF (38/602 Pages) Motorola, Inc – ENHANCED 32-BIT MICROPROCESSOR

Introduction
1.8 PIPELINED ARCHITECTURE
The MC68030 uses a three-stage pipelined internal architecture to provide for optimum
instruction throughput. The pipeline allows as many as three words of a single instruction or
three consecutive instructions to be decoded concurrently.
1.9 THE CACHE MEMORIES
Due to locality of reference, instructions and data that are used in a program have a high
probability of being reused within a short time. Additionally, instructions and data operands
that reside in proximity to the instructions and data currently in use also have a high
probability of being utilized within a short period. To exploit these locality characteristics, the
MC68030 contains two on-chip logical caches, a data cache, and an instruction cache.
Each of the caches stores 256 bytes of information, organized as 16 entries, each containing
a block of four long words (16 bytes). The processor fills the cache entries either one long
word at a time or, during burst mode accesses, four long words consecutively. The burst
mode of operation not only fills the cache efficiently but also captures adjacent instruction or
data items that are likely to be required in the near future due to locality characteristics of
the executing task.
The caches improve the overall performance of the system by reducing the number of bus
cycles required by the processor to fetch information from memory and by increasing the
bus bandwidth available for other bus masters in the system. Addition of the data cache in
the MC68030 extends the benefits of cache techniques to all memory accesses. During a
write cycle, the data cache circuitry writes data to a cached data item as well as to the item
in memory, maintaining consistency between data in the cache and that in memory.
However, writing data that is not in the cache may or may not cause the data item to be
stored in the cache, depending on the write allocation policy selected in the cache control
register (CACR).
MOTOROLA
MC68030 USER’S MANUAL
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