PIC24HJ16GP304-E Datasheet, PDF (29/274 Pages) Microchip Technology – High-Performance, 16-bit Microcontrollers

PIC24HJ32GP202/204 AND PIC24HJ16GP304
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 is shown in
Figure 4-3.
All Effective Addresses (EAs) in the data memory space
are 16 bits wide and point to the bytes within the data
space. This arrangement gives a data space address
range of 64 Kbytes or 32K words. The lower half of the
data memory space (that is, when EA<15> = 0) is used
for implemented memory addresses, while the upper
half (EA<15> = 1) is reserved for the Program Space
Visibility area (see Section 4.4.3 “Reading Data from
Program Memory Using Program Space Visibility”).
PIC24HJ32GP202/204 and PIC24HJ16GP304
devices implement up to 2 Kbytes of data memory.
Should an EA point to a location outside of this area, an
all-zero word or byte will be 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.
4.2.2
DATA MEMORY ORGANIZATION
AND ALIGNMENT
To maintain backward compatibility with PIC^® devices
and improve data space memory usage efficiency, the
PIC24HJ32GP202/204 and PIC24HJ16GP304 instruc-
tion 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 recog-
nizes 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.
Data byte reads will read 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 when 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 instruction
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
Least Significant Byte. The Most Significant Byte is not
modified.
A sign-extend instruction (SE) is provided to allow
users 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 2 Kbytes of the Near Data Space, from 0x0000
to 0x07FF, is primarily occupied by Special Function
Registers (SFRs). These are used by the
PIC24HJ32GP202/204 and PIC24HJ16GP304 core
and peripheral modules to control 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’. A complete listing of implemented
SFRs, including their addresses, is shown in Table 4-1
through Table 4-22.
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.
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 via 13-bit absolute
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.
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DS70289H-page 29