DSP56303 FREESCALE [Freescale Semiconductor, Inc], DSP56303 Datasheet - Page 46

• Manufacturer Part Number: DSP56303
• Manufacturer: FREESCALE [Freescale Semiconductor, Inc]

Memory Configuration
3.1.1 Internal Program Memory
The default internal program memory consists of a 24-bit-wide, high-speed, SRAM occupying
the lowest 4 K (default), 3 K, 2 K, or 1 K locations in program memory space, depending on the
settings of the OMR[MS] and (SR[CE]) bits. Section 4.3.2, Operating Mode Register (OMR), on
page 1-15 provides details on the MS bit. Section 4.3.1, Status Register (SR), on page 1-9
provides details on the CE bit. The default internal program RAM is organized in 16 banks with
256 locations each (4 K). Setting the MS bit switches four banks of program memory to the X
data memory and an additional four banks of program memory to the Y data memory. Setting the
CE bit switches four banks of internal program memory to the Instruction Cache and reassigns its
address to external program memory. The memory addresses for the Instruction Cache vary
depending on the setting of the MS and CE bits. Section 3.6 provides a summary of the internal
RAM configurations. Refer to the memory maps for detailed information.
3.1.2 Memory Switch Modes—Program Memory
Memory switch mode allows reallocation of portions of program RAM to X and Y data RAM.
OMR[7] is the memory switch (MS) bit that controls this function, as follows:
3.1.3 Instruction Cache
In program memory space, the location of the internal Instruction Cache (when enabled by the
CE bit) varies depending on the setting of the MS bit, as noted above. Refer to the memory maps
for detailed address information. When the instruction cache is enabled (that is, the SR[CE] bit is
set), 1 K program words switch to instruction cache and are not accessible via addressing; the
address range switches to external program memory.
3.1.4 Program Bootstrap ROM
The program memory space occupying locations $FF0000–$FF00BF includes the internal
bootstrap ROM. This ROM contains the 192-word DSP56303 bootstrap program.
3-2
When the MS bit is cleared, program memory consists of the default 4 K × 24-bit memory
space described in the previous section. In this default mode, the lowest external program
memory location is $1000. If the CE bit is set, the program memory consists of the lowest
3 K × 24-bits of memory space and the lowest external program memory location is
$0C00.
When the MS bit is set, the highest 2 K × 24-bit portion of the internal program memory is
switched to internal X and Y data memory. In this mode, the lowest external program
memory location is $800. If the CE bit is set and the MS bit is set, the program memory
consists of the lowest 1 K × 24-bits of memory space and the lowest external program
memory location is $400.
DSP56303 User’s Manual, Rev. 2
Freescale Semiconductor