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MOTOROLA
MC68349 USER’S MANUAL
5- 1
SECTION 5
CPU030
The MC68349 is based on the CPU030 processor, which combines a full 32-bit central
processor (CPU32+) with a configurable instruction cache (CIC) and a quad data memory
module (QDMM). This section discusses the CPU32+ and the CIC. The QDMM is
discussed in Section 6 Quad Data Memory Module.
The CPU32+, the second instruction processing module of the M68300 family, is based
on the industry-standard MC68000 core processor. Like the original CPU32, it has many
features of the MC68010 and MC68020 as well as unique features suited for high-
performance processor applications. The CPU32+ provides a significant performance
increase over the MC68000 CPU, yet maintains source-code and binary-code
compatibility with the M68000 family. The CPU32+ differs from the original CPU32 in two
ways: it allows an option of a 32-bit data bus interface and allows byte-misaligned
accesses to data operands.
The CIC improves system performance by reducing average memory access times for all
instruction accesses (cache mode) and by providing fast static random access memory
(SRAM) storage for critical data structures or code sequences (SRAM mode). The
CPU32+ is connected directly to the CIC instead of through the intermodule bus (IMB);
this direct connection reduces the impact of direct memory access (DMA) operations on
system performance by allowing CPU32+ accesses to the CIC and DMA transfers on the
IMB to occur simultaneously.
5.1 CPU32+ OVERVIEW
The CPU32+ is designed to interface to the intermodule bus, allowing interaction with
other IMB submodules. In this manner, integrated processors can be developed that
contain useful peripherals on chip. This integration provides high-speed accesses among
the IMB submodules, increasing system performance.
The CPU32+ core is a CPU32 core with its bus interface unit modified to connect directly
to the 32-bit IMB and take advantage of the larger bus width. Although the original CPU32
core already had a 32-bit internal data path and 32-bit arithmetic hardware, its external
interface (i.e., to the internal IMB) was 16 bits. The CPU32+ core, however, can operate
on 32-bit external operands with one bus cycle. This capability allows the CPU32+ core to
fetch a long-word instruction or two word-length instructions in one bus cycle, allowing the
internal instruction queue to be filled more quickly. The CPU32+ core can also read and
write 32-bits of data in one bus cycle. The CPU32+ has an additional word in its