Microchip Technology MA330025-1 Data Sheet
2009-2012 Microchip Technology Inc.
DS70616G-page 49
dsPIC33EPXXX(GP/MC/MU)806/810/814 and PIC24EPXXX(GP/GU)810/814
4.2
Data Address Space
The CPU has a separate 16-bit wide data memory
space. The data space is accessed using separate
Address Generation Units (AGUs) for read and write
operations. The data memory maps are shown in
space. The data space is accessed using separate
Address Generation Units (AGUs) for read and write
operations. The data memory maps are shown in
.
All Effective Addresses (EAs) in the data memory space
are 16 bits wide and point to bytes within the data space.
This arrangement gives a Base Data Space address
range of 64 Kbytes or 32K words.
The Base Data Space address is used in conjunction
with a Read or Write Page register (DSRPAG or
DSWPAG) to form an Extended Data Space, which has
a total address range of 16 MBytes.
dsPIC33EPXXX(GP/MC/MU)806/810/814 and
PIC24EPXXX(GP/GU)810/814 devices implement up
to 56 Kbytes of data memory. If an EA point to a loca-
tion outside of this area, an all-zero word or byte is
returned.
are 16 bits wide and point to bytes within the data space.
This arrangement gives a Base Data Space address
range of 64 Kbytes or 32K words.
The Base Data Space address is used in conjunction
with a Read or Write Page register (DSRPAG or
DSWPAG) to form an Extended Data Space, which has
a total address range of 16 MBytes.
dsPIC33EPXXX(GP/MC/MU)806/810/814 and
PIC24EPXXX(GP/GU)810/814 devices implement up
to 56 Kbytes of data memory. If an EA point to a loca-
tion outside of this area, an all-zero word or byte is
returned.
4.2.1
DATA SPACE WIDTH
The data memory space is organized in byte-
addressable, 16-bit wide blocks. Data is aligned in
data memory and registers as 16-bit words, but all data
space EAs resolve to bytes. The Least Significant
Bytes (LSBs) of each word have even addresses, while
the Most Significant Bytes (MSBs) have odd
addresses.
addressable, 16-bit wide blocks. Data is aligned in
data memory and registers as 16-bit words, but all data
space EAs resolve to bytes. The Least Significant
Bytes (LSBs) of each word have even addresses, while
the Most Significant Bytes (MSBs) have odd
addresses.
4.2.2
DATA MEMORY ORGANIZATION
AND ALIGNMENT
AND ALIGNMENT
To maintain backward compatibility with PIC
®
MCU
devices and improve data space memory usage
efficiency, the device instruction set supports both word
and byte operations. As a consequence of byte
accessibility, all Effective Address calculations are
internally scaled to step through word-aligned memory.
For example, the core recognizes that Post-Modified
Register Indirect Addressing mode [Ws++] results in a
value of Ws + 1 for byte operations and Ws + 2 for word
operations.
A data byte read, reads the complete word that
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 data path. 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 that matches
the byte address.
efficiency, the device instruction set supports both word
and byte operations. As a consequence of byte
accessibility, all Effective Address calculations are
internally scaled to step through word-aligned memory.
For example, the core recognizes that Post-Modified
Register Indirect Addressing mode [Ws++] results in a
value of Ws + 1 for byte operations and Ws + 2 for word
operations.
A data byte read, reads the complete word that
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 data path. 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 that matches
the byte address.
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
operations, or translating from 8-bit MCU code. If a
misaligned read or write is attempted, an address error
trap is generated. If the error occurred on a read, the
instruction underway is completed. If the error occurred
on a write, the instruction is executed but the write does
not occur. In either case, a trap is then executed,
allowing the system and/or user application to examine
the machine state prior to execution of the address
Fault.
All byte loads into any W register are loaded into the
LSB. The MSB is not modified.
A Sign-Extend instruction (SE) is provided to allow user
applications to translate 8-bit signed data to 16-bit
signed values. Alternatively, for 16-bit unsigned data,
user applications can clear the MSB of any W register
by executing a Zero-Extend (ZE) instruction on the
appropriate address.
Misaligned word data fetches are not supported, so
care must be taken when mixing byte and word
operations, or translating from 8-bit MCU code. If a
misaligned read or write is attempted, an address error
trap is generated. If the error occurred on a read, the
instruction underway is completed. If the error occurred
on a write, the instruction is executed but the write does
not occur. In either case, a trap is then executed,
allowing the system and/or user application to examine
the machine state prior to execution of the address
Fault.
All byte loads into any W register are loaded into the
LSB. The MSB is not modified.
A Sign-Extend instruction (SE) is provided to allow user
applications to translate 8-bit signed data to 16-bit
signed values. Alternatively, for 16-bit unsigned data,
user applications can clear the MSB of any W register
by executing a Zero-Extend (ZE) instruction on the
appropriate address.
4.2.3
SFR SPACE
The first 4 Kbytes of the Near Data Space, from 0x0000
to 0x0FFF, is primarily occupied by Special Function
Registers (SFRs). These are used by the core and
peripheral modules for controlling the operation of the
device.
SFRs are distributed among the modules that they
control and are generally grouped together by module.
Much of the SFR space contains unused addresses;
these are read as ‘0’.
to 0x0FFF, is primarily occupied by Special Function
Registers (SFRs). These are used by the core and
peripheral modules for controlling the operation of the
device.
SFRs are distributed among the modules that they
control and are generally grouped together by module.
Much of the SFR space contains unused addresses;
these are read as ‘0’.
4.2.4
NEAR DATA SPACE
The 8-Kbyte area between 0x0000 and 0x1FFF is
referred to as the Near Data Space. Locations in this
space are directly addressable through a 13-bit abso-
lute address field within all memory direct instructions.
Additionally, the whole data space is addressable using
MOV instructions, which support Memory Direct
Addressing mode with a 16-bit address field, or by
using Indirect Addressing mode using a working
register as an Address Pointer.
referred to as the Near Data Space. Locations in this
space are directly addressable through a 13-bit abso-
lute address field within all memory direct instructions.
Additionally, the whole data space is addressable using
MOV instructions, which support Memory Direct
Addressing mode with a 16-bit address field, or by
using Indirect Addressing mode using a working
register as an Address Pointer.
Note:
The actual set of peripheral features and
interrupts varies by the device. Refer to
the corresponding device tables and
pinout diagrams for device-specific
information.
interrupts varies by the device. Refer to
the corresponding device tables and
pinout diagrams for device-specific
information.