Datasheet

dsPIC30F6011A/6012A/6013A/6014A
DS70143E-page 34 © 2011 Microchip Technology Inc.
FIGURE 3-9: DATA SPACE FOR MCU AND DSP (MAC CLASS) INSTRUCTIONS EXAMPLE
TABLE 3-2: EFFECT OF INVALID
MEMORY ACCESSES
All effective addresses are 16 bits wide and point to
bytes within the data space. Therefore, the data space
address range is 64 Kbytes or 32K words.
3.2.3 DATA SPACE WIDTH
The core data width is 16 bits. All internal registers are
organized as 16-bit wide words. Data space memory is
organized in byte addressable, 16-bit wide blocks.
3.2.4 DATA ALIGNMENT
To help maintain backward compatibility with PIC
®
MCU devices and improve data space memory usage
efficiency, the dsPIC30F instruction set supports both
word and byte operations. Data is aligned in data mem-
ory and registers as words, but all data space EAs
resolve to bytes. Data byte reads will read the complete
word which contains the byte, using the LSb of any EA
to determine which byte to select. The selected byte is
placed onto the LSB of the X data path (no byte
accesses are possible from the Y data path as the MAC
class of instruction can only fetch words). That is, data
memory and registers are organized as two parallel
byte wide entities with shared (word) address decode
but separate write lines. Data byte writes only write to
the corresponding side of the array or register which
matches the byte address.
As a consequence of this byte accessibility, all Effective
Address calculations (including those generated by the
DSP operations which are restricted to word-sized
data) are internally scaled to step through word aligned
memory. For example, the core would recognize that
Post-Modified Register Indirect Addressing mode
[Ws++] will result in a value of Ws + 1 for byte
operations and Ws + 2 for word operations.
SFR SPACE
(Y SPACE)
X SPACE
SFR SPACE
UNUSED
X SPACE
X SPACE
Y SPACE
UNUSED
UNUSED
Non-MAC Class Ops (Read) MAC Class Ops (Read)
Indirect EA from any W Indirect EA from W10, W11 Indirect EA from W8, W9
Attempted Operation Data Returned
EA = an unimplemented address 0x0000
(1)
W8 or W9 used to access Y data
space in a MAC instruction
0x0000
W10 or W11 used to access X
data space in a MAC instruction
0x0000
Note 1: An address error trap is generated when
an unimplemented memory address is
accessed.