DSP56303 FREESCALE [Freescale Semiconductor, Inc], DSP56303 Datasheet - Page 47

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

3.2 X Data Memory Space
The X data memory space consists of the following:
Note:
3.2.1 Internal X Data Memory
The default internal X data RAM is a 24-bit-wide, internal, static memory occupying the lowest
2 K locations ($000–$7FF) in X memory space. The internal X data RAM is organized into 8
banks with 256 locations each. Available X data memory space is increased by 1 K through
reallocation of program memory using the memory switch mode described in the next section.
3.2.2 Memory Switch Modes—X Data Memory
Memory switch mode reallocates portions of program RAM to X and Y data memory. Bit 7 in the
OMR is the MS bit that controls this function, as follows:
3.2.3 Internal I/O Space—X Data Memory
One part of the internal peripheral registers and some of the DSP56303 core registers occupy the
top 128 locations of the X data memory ($FFFF80–$FFFFFF). This area is referred to as the
internal X I/O space and it can be accessed by move, movep instructions and by bit-oriented
instructions (bchg, bclr, bset, btst, brclr, brset, bsclr, bsset, jclr, jset, jsclr, and jsset). The
contents of the internal X I/O memory space are listed in Appendix A, Bootstrap Program.
Freescale Semiconductor
Internal X data memory (2 K by default up to 3 K)
Internal I/O space (upper 128 locations)
Optional off-chip memory expansion (up to 64 K in 16-bit mode, or 256 K in 24-bit mode
using the 18 external address lines, or 4 M using the external address lines and the four
address attribute lines). Refer to the DSP56300 Family Manual, especially Chapter 9,
External Memory Interface (Port A), for details on using the external memory interface to
access external X data memory.
When the MS bit is cleared, the X data memory consists of the default 2 K × 24-bit
memory space described in the previous section. In this default mode, the lowest external
X data memory location is $800.
When the MS bit is set, a portion of the higher locations of the internal program memory is
switched to X and Y data memory. The X data memory in this mode consists of a
3 K × 24-bit memory space. In this mode, the lowest external X data memory location is
$C00.
The X memory space at $FF0000–$FFEFFF is reserved and should not be accessed.
DSP56303 User’s Manual, Rev. 2
X Data Memory Space
3-3