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5- 6
MC68349 USER’S MANUAL
MOTOROLA
5.1.6 Addressing Modes
Addressing in the CPU32+ is register oriented. Most instructions allow the results of the
specified operation to be placed either in a register or directly in memory; this flexibility
eliminates the need for extra instructions to store register contents in memory.
The seven basic addressing modes are as follows:
Register Direct
Register Indirect
Register Indirect with Index
Program Counter Indirect with Displacement
Program Counter Indirect with Index
Absolute
Immediate
Included in the register indirect addressing modes are the capabilities to postincrement,
predecrement, and offset. The PC relative mode also has index and offset capabilities. In
addition to these addressing modes, many instructions implicitly specify the use of the SR,
SP and/or PC. Addressing is explained fully in the M68000PM/AD,
M68000 Family
Programmer’s Reference Manual.
5.2 CONFIGURABLE INSTRUCTION CACHE OVERVIEW
The CIC contains four dual-purpose memory blocks which can be independently
configured as either instruction cache or SRAM. When configured as cache, each block
provides 256 bytes of instruction cache, for a maximum 1-kbyte cache. The instruction
cache improves system performance by providing cached instructions to the CPU32+ with
very low latency. Alternatively, each element can be used as 512 bytes of SRAM, for a
maximum of 2-kbytes SRAM. When configured as SRAM, the CIC provides a fast memory
for general storage of data and/or instructions. The functionality of the blocks is
independently programmable to allow a mix of instruction cache and SRAM for different
applications. A high-level system diagram is shown in Figure 5-3.
A key feature of the CIC is its direct data path to the CPU32+. CPU accesses to the CIC
do not require use of the IMB, resulting in increased IMB bandwidth available to other bus
masters such as the DMA controller. This direct connection helps minimize the impact of
DMA activity on CPU performance. The direct data path prevents accesses to the CIC by
other modules on the IMB; hence, the CIC cannot be accessed from the IMB by the DMA
controller.