MOTOROLA
MC68349 USER'S MANUAL
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1.3.2 Configurable Instruction Cache (CIC)
The configurable instruction cache is a highly configurable memory resource designed to
optimize the supply of instructions to the CPU32+. The CIC is closely coupled with the
CPU32+, yet isolated from the IMB, allowing the processor to continue instruction
execution while a DMA controller or other bus master occupies the external bus. The CIC
also moderates power consumption by reducing off-chip accesses.
The CIC is composed of four identical blocks each of which can be independently
configured as a 256-byte instruction cache or as a 512-byte static random access memory
(SRAM). Either instructions or operands can be stored in the SRAM. When configured as
SRAM, a block is independently relocatable in the system's address space. When
configured as a cache, a block operates as a direct-mapped cache of sixty-four 32-bit
entries. When multiple blocks are configured as caches, set-associativity is supported up
to a maximum of four sets. Each cache block can be independently locked to freeze its
internal contents.
Using CIC flexibility, it is feasible to place high-priority interrupt or operating system
routines in protected SRAM, which is always instantly available, while allowing remaining
blocks to operate as caches to increase the performance of general system and user
tasks. The CIC configuration can be established at system initialization or on a task-by-
task basis, yielding maximum flexibility.
1.3.3 Quad Data Memory Module (QDMM)
The QDMM provides dedicated data storage resources for the CPU030 in the form of four
independent 1-Kbyte SRAM blocks. Each of these blocks can be independently relocated
anywhere in the system address space, and each is independently protected
(supervisor/user, read/write).
The QDMM can be used as scratchpad memory, stack caches for independent tasks,
buffers for I/O operations, or parameter storage. The QDMM provides significant
performance and power-management benefits to MC68349-based systems. As general
SRAM, this space can also contain instructions for fast access to additional interrupt
handlers, operating system code, algorithms, or other frequently accessed routines. A
total of 4096 bytes of SRAM is provided in the QDMM.
1.4 ON-CHIP PERIPHERALS
To improve total system throughput and reduce part count, board size, and cost of system
implementation, the M68300 family integrates on-chip, intelligent peripheral modules and
typical glue logic. These functions on the MC68349 include the SIM49, a DMA controller,
and a serial module.
The processor communicates with these modules over the on-chip intermodule bus (IMB).
This backbone of the chip is similar to traditional external buses with address, data, clock,
interrupt, arbitration, and handshake signals. Because bus masters (like the CPU32+ and
DMA), peripherals, and the SIM49 are all on the chip, the IMB ensures that