Motorola DSP56301 - Manual (Page 64)

Y Data Memory Space
3 -4 DSP56301 User’s Manual
3.2.3 Internal I/O Space—X Data Memory
One part of the on-chip peripheral registers and some of the DSP56301 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 Section B.1 in Appendix B.
3.3 Y Data Memory Space
The Y data memory space consists of the following:
n Internal Y data memory (2 K by default up to 3 K)
n External 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 Y data memory.
Note: The Y memory space at $FF0000–$FFEFFF is reserved and should not be
accessed.
3.3.1 Internal Y Data Memory
The default on-chip Y data RAM is a 24-bit-wide, internal, static memory occupying the
lowest 2 K ($000–$7FF) of Y memory space. The on-chip Y data RAM is organized into 8
banks with 256 locations each. Available Y data memory space is increased by 1 K through
reallocation of program memory using the memory switch mode described in the next section.
3.3.2 Memory Switch Modes—Y Data Memory
Memory switch mode reallocates of 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 Y data memory consists of the default 2 K
×
24-bit
memory space described in the previous section. In this default mode, the lowest
external Y 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 Y data memory in this mode
consists of a 3 K
×
24-bit memory space. In this mode, the lowest external Y data
memory location is $C00.