70592C Datasheet, PDF (58/314 Pages) Microchip Technology – High-Performance, 16-bit Microcontrollers

PIC24HJXXXGPX06A/X08A/X10A
TABLE 4-34: FUNDAMENTAL ADDRESSING MODES SUPPORTED
Addressing Mode
Description
File Register Direct
The address of the file register is specified explicitly.
Register Direct
The contents of a register are accessed directly.
Register Indirect
The contents of Wn forms the EA.
Register Indirect Post-Modified
The contents of Wn forms the EA. Wn is post-modified (incremented or
decremented) by a constant value.
Register Indirect Pre-Modified
Wn is pre-modified (incremented or decremented) by a signed constant value
to form the EA.
Register Indirect with Register Offset The sum of Wn and Wb forms the EA.
Register Indirect with Literal Offset The sum of Wn and a literal forms the EA.
4.3.3 MOVE INSTRUCTIONS
Move instructions provide a greater degree of address-
ing flexibility than other instructions. In addition to the
Addressing modes supported by most MCU instruc-
tions, move instructions also support Register Indirect
with Register Offset Addressing mode, also referred to
as Register Indexed mode.
Note:
For the MOV instructions, the Addressing
mode specified in the instruction can differ
for the source and destination EA.
However, the 4-bit Wb (Register Offset)
field is shared between both source and
destination (but typically only used by
one).
In summary, the following Addressing modes are
supported by move instructions:
• Register Direct
• Register Indirect
• Register Indirect Post-modified
• Register Indirect Pre-modified
• Register Indirect with Register Offset (Indexed)
• Register Indirect with Literal Offset
• 8-bit Literal
• 16-bit Literal
Note:
Not all instructions support all the
Addressing modes given above.
Individual instructions may support
different subsets of these Addressing
modes.
4.3.4 OTHER INSTRUCTIONS
Besides the various addressing modes outlined above,
some instructions use literal constants of various sizes.
For example, BRA (branch) instructions use 16-bit
signed literals to specify the branch destination directly,
whereas the DISI instruction uses a 14-bit unsigned
literal field. In some instructions, the source of an oper-
and or result is implied by the opcode itself. Certain
operations, such as NOP, do not have any operands.
4.4 Interfacing Program and Data
Memory Spaces
The PIC24HJXXXGPX06A/X08A/X10A architecture
uses a 24-bit wide program space and a 16-bit wide
data space. The architecture is also a modified Harvard
scheme, meaning that data can also be present in the
program space. To use this data successfully, it must
be accessed in a way that preserves the alignment of
information in both spaces.
Aside
from
normal
execution,
the
PIC24HJXXXGPX06A/X08A/X10A architecture pro-
vides two methods by which program space can be
accessed during operation:
• Using table instructions to access individual bytes
or words anywhere in the program space
• Remapping a portion of the program space into
the data space (Program Space Visibility)
Table instructions allow an application to read or write
to small areas of the program memory. This capability
makes the method ideal for accessing data tables that
need to be updated from time to time. It also allows
access to all bytes of the program word. The remap-
ping method allows an application to access a large
block of data on a read-only basis, which is ideal for
look ups from a large table of static data. It can only
access the least significant word of the program word.
4.4.1 ADDRESSING PROGRAM SPACE
Since the address ranges for the data and program
spaces are 16 and 24 bits, respectively, a method is
needed to create a 23-bit or 24-bit program address
from 16-bit data registers. The solution depends on the
interface method to be used.
For table operations, the 8-bit Table Page register
(TBLPAG) is used to define a 32K word region within
the program space. This is concatenated with a 16-bit
EA to arrive at a full 24-bit program space address. In
this format, the Most Significant bit of TBLPAG is used
to determine if the operation occurs in the user memory
(TBLPAG<7> = 0) or the configuration memory
(TBLPAG<7> = 1).
DS70592C-page 58
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