Motorola DSP56301 - Manual (Page 63)

X Data Memory Space
Memory Configuration 3 -3
3.1.4 Program Bootstrap ROM
In the current version of the DSP56301, the program memory space occupying locations
$FF0000–$FF0C00 contains the 3 K-word DSP56301 bootstrap program space.
Note: In older versions of the DSP56301, the program memory space occupying
locations $FF0000–$FF00BF contains the 192-word DSP56301 bootstrap
program.
3.2 X Data Memory Space
The X data memory space consists of the following:
n Internal X data memory (2 K by default up to 3 K)
n Internal I/O space (upper 128 locations)
n Optional off-chip memory expansion (up to 64 K in 16-bit mode or 16 M in 24-bit
mode). 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.
Note: The X memory space at $FF0000–$FFEFFF is reserved and should not be
accessed.
3.2.1 Internal X Data Memory
The default on-chip X data RAM is a 24-bit-wide, internal, static memory in the lowest 2 K
locations ($000–$7FF) in X memory space. The on-chip 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:
n 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.
n 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.