Microchip Technology MA300015 Data Sheet
dsPIC30F6010A/6015
DS70150E-page 30
© 2011 Microchip Technology Inc.
3.2.2
DATA SPACES
The X data space is used by all instructions and sup-
ports all addressing modes. There are separate read
and write data buses. The X read data bus is the return
data path for all instructions that view data space as
combined X and Y address space. It is also the X
address space data path for the dual operand read
instructions (MAC class). The X write data bus is the
only write path to data space for all instructions.
ports all addressing modes. There are separate read
and write data buses. The X read data bus is the return
data path for all instructions that view data space as
combined X and Y address space. It is also the X
address space data path for the dual operand read
instructions (MAC class). The X write data bus is the
only write path to data space for all instructions.
The X data space also supports Modulo Addressing for
all instructions, subject to addressing mode restric-
tions. Bit-Reversed Addressing is only supported for
writes to X data space.
all instructions, subject to addressing mode restric-
tions. Bit-Reversed Addressing is only supported for
writes to X data space.
The Y data space is used in concert with the X data
space by the MAC class of instructions (CLR, ED, EDAC,
MAC
space by the MAC class of instructions (CLR, ED, EDAC,
MAC
, MOVSAC, MPY, MPY.N and MSC) to provide two
concurrent data read paths. No writes occur across the
Y bus. This class of instructions dedicates two W reg-
ister pointers, W10 and W11, to always address Y data
space, independent of X data space, whereas W8 and
W9 always address X data space. Note that during
accumulator write-back, the data address space is con-
sidered a combination of X and Y data spaces, so the
write occurs across the X bus. Consequently, the write
can be to any address in the entire data space.
Y bus. This class of instructions dedicates two W reg-
ister pointers, W10 and W11, to always address Y data
space, independent of X data space, whereas W8 and
W9 always address X data space. Note that during
accumulator write-back, the data address space is con-
sidered a combination of X and Y data spaces, so the
write occurs across the X bus. Consequently, the write
can be to any address in the entire data space.
The Y data space can only be used for the data
prefetch operation associated with the MAC class of
instructions. It also supports Modulo Addressing for
automated circular buffers. Of course, all other instruc-
tions can access the Y data address space through the
X data path, as part of the composite linear space.
prefetch operation associated with the MAC class of
instructions. It also supports Modulo Addressing for
automated circular buffers. Of course, all other instruc-
tions can access the Y data address space through the
X data path, as part of the composite linear space.
The boundary between the X and Y data spaces is
defined as shown in
defined as shown in
and is not user pro-
grammable. Should an EA point to data outside its own
assigned address space, or to a location outside phys-
ical memory, an all-zero word/byte will be returned. For
example, although Y address space is visible by all
non-MAC instructions using any addressing mode, an
attempt by a MAC instruction to fetch data from that
space, using W8 or W9 (X space pointers), will return
0x0000.
assigned address space, or to a location outside phys-
ical memory, an all-zero word/byte will be returned. For
example, although Y address space is visible by all
non-MAC instructions using any addressing mode, an
attempt by a MAC instruction to fetch data from that
space, using W8 or W9 (X space pointers), will return
0x0000.
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.
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.
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
®
devices and improve data space memory usage effi-
ciency, 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.
ciency, 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.
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.
All word accesses must be aligned to an even address.
Misaligned word data fetches are not supported, so
care must be taken when mixing byte and word opera-
tions, or translating from 8-bit MCU code. Should a
misaligned read or write be attempted, an address
error trap will be generated. If the error occurred on a
read, the instruction underway is completed, whereas if
it occurred on a write, the instruction will be executed
but the write will not occur. In either case, a trap will
then be executed, allowing the system and/or user to
examine the machine state prior to execution of the
address Fault.
Misaligned word data fetches are not supported, so
care must be taken when mixing byte and word opera-
tions, or translating from 8-bit MCU code. Should a
misaligned read or write be attempted, an address
error trap will be generated. If the error occurred on a
read, the instruction underway is completed, whereas if
it occurred on a write, the instruction will be executed
but the write will not occur. In either case, a trap will
then be executed, allowing the system and/or user to
examine the machine state prior to execution of the
address Fault.
FIGURE 3-8:
DATA ALIGNMENT
TABLE 3-2:
EFFECT OF INVALID
MEMORY ACCESSES
MEMORY ACCESSES
Attempted Operation
Data Returned
EA = an unimplemented address
0x0000
W8 or W9 used to access Y data
space in a MAC instruction
space in a MAC instruction
0x0000
W10 or W11 used to access X
data space in a MAC instruction
data space in a MAC instruction
0x0000
15
8 7
0
0001
0003
0005
0000
0002
0004
Byte 1 Byte 0
Byte 3 Byte 2
Byte 5 Byte 4
LSB
MSB