PIC18F4539 Datasheet, PDF (41/322 Pages) Microchip Technology – Enhanced FLASH Microcontrollers with Single Phase Induction Motor Control Kernel

4.9 Data Memory Organization
The data memory is implemented as static RAM. Each
register in the data memory has a 12-bit address,
allowing up to 4096 bytes of data memory. The data
memory map is divided into 16 banks that contain 256
bytes each. The lower 4 bits of the Bank Select Regis-
ter (BSR<3:0>) select which bank will be accessed.
The upper 4 bits for the BSR are not implemented.
The data memory contains Special Function Registers
(SFRs) and General Purpose Registers (GPRs). The
SFRs are used for control and status of the controller
and peripheral functions, while GPRs are used for data
storage and scratch pad operations in the user’s appli-
cation. The SFRs start at the last location of Bank 15
(FFFh) and extend downwards. Any remaining space
beyond the SFRs in the Bank may be implemented as
GPRs. GPRs start at the first location of Bank 0 and
grow upwards. Any read of an unimplemented location
will read as ‘0’s.
The organization of the data memory space for these
devices is shown in Figure 4-5 and Figure 4-6.
PIC18FX439 devices have 640 bytes of data RAM,
extending from Bank 0 to Bank 2 (000h through 27Fh).
The block of 128 bytes above this to the top of the bank
(280h to 2FFh) is used as data memory for the Motor
Control kernel, and is not available to the user. Reading
these locations will return random information that
reflects the kernel’s “scratch” data. Modifying the data
in these locations may disrupt the operation of the
ProMPT kernel.
PIC18FX539 devices have 1408 bytes of data RAM,
extending from Bank 0 to Bank 5 (000h through 57Fh).
As with the PIC18FX439 devices, the block of
128 bytes above this to the end of the bank (580h to
5FFh) is used by the Motor Control kernel.
The entire data memory may be accessed directly or
indirectly. Direct addressing may require the use of the
BSR register. Indirect addressing requires the use of a
File Select Register (FSRn) and a corresponding Indi-
rect File Operand (INDFn). Each FSR holds a 12-bit
address value that can be used to access any location
in the Data Memory map without banking.
The instruction set and architecture allow operations
across all banks. This may be accomplished by indirect
addressing, or by the use of the MOVFF instruction. The
MOVFF instruction is a two-word/two-cycle instruction
that moves a value from one register to another.
To ensure that commonly used registers (SFRs and
select GPRs) can be accessed in a single cycle,
regardless of the current BSR values, an Access Bank
is implemented. A segment of Bank 0 and a segment of
Bank 15 comprise the Access RAM. Section 4.10
provides a detailed description of the Access RAM.
PIC18FXX39
4.9.1
GENERAL PURPOSE REGISTER
FILE
The register file can be accessed either directly or indi-
rectly. Indirect addressing operates using a File Select
Register and corresponding Indirect File Operand. The
operation of indirect addressing is shown in
Section 4.12.
Enhanced MCU devices may have banked memory in
the GPR area. GPRs are not initialized by a Power-on
Reset and are unchanged on all other RESETS.
Data RAM is available for use as GPR registers by all
instructions. The top half of Bank 15 (F80h to FFFh)
contains SFRs. All other banks of data memory contain
GPR registers, starting with Bank 0.
4.9.2 SPECIAL FUNCTION REGISTERS
The Special Function Registers (SFRs) are registers
used by the CPU and Peripheral Modules for control-
ling the desired operation of the device. These regis-
ters are implemented as static RAM. A list of these
registers is given in Table 4-1 and Table 4-2.
The SFRs can be classified into two sets; those asso-
ciated with the “core” function and those related to the
peripheral functions. Those registers related to the
“core” are described in this section, while those related
to the operation of the peripheral features are
described in the section of that peripheral feature.
The SFRs are typically distributed among the
peripherals whose functions they control. The unused
SFR locations will be unimplemented and read as '0's.
See Table 4-1 for addresses for the SFRs.
Note:
In this chapter and throughout this docu-
ment, certain SFR names and individual
bits are marked with an asterisk (*). This
denotes registers that are not implemented
in PIC18FXX39 devices, but whose names
are retained to maintain compatibility with
PIC18FXX2 devices. The designated bits
within these registers are reserved and
may be used by certain modules or the
Motor Control kernel. Users should not
write to these registers or alter these bit
values. Failure to do this may result in
erratic microcontroller operation.
 2002 Microchip Technology Inc.
Preliminary
DS30485A-page 39