PIC18F97J60 Datasheet, PDF (91/474 Pages) Microchip Technology – 64/80/100-Pin, High-Performance, 1 Mbit Flash Microcontrollers with Ethernet

PIC18F97J60 FAMILY
5.4.3.1
FSR Registers and the
INDF Operand
At the core of Indirect Addressing are three sets of
registers: FSR0, FSR1 and FSR2. Each represents a
pair of 8-bit registers: FSRnH and FSRnL. The four
upper bits of the FSRnH register are not used, so each
FSR pair holds a 12-bit value. This represents a value
that can address the entire range of the data memory
in a linear fashion. The FSR register pairs, then, serve
as pointers to data memory locations.
Indirect Addressing is accomplished with a set of Indirect
File Operands: INDF0 through INDF2. These can be
thought of as “virtual” registers; they are mapped in the
SFR space but are not physically implemented. Reading
or writing to a particular INDF register actually accesses
its corresponding FSR register pair. A read from INDF1,
for example, reads the data at the address indicated by
FSR1H:FSR1L. Instructions that use the INDF registers
as operands actually use the contents of their
corresponding FSR as a pointer to the instruction’s
target. The INDF operand is just a convenient way of
using the pointer.
Because Indirect Addressing uses a full 12-bit address,
data RAM banking is not necessary. Thus, the current
contents of the BSR and Access RAM bit have no effect
on determining the target address.
FIGURE 5-9:
INDIRECT ADDRESSING
Using an instruction with one of the
Indirect Addressing registers as the
operand....
ADDWF, INDF1, 1
...uses the 12-bit address stored in
the FSR pair associated with that
register....
FSR1H:FSR1L
7
07
0
xxxx1111 11001100
...to determine the data memory
location to be used in that operation.
In this case, the FSR1 pair contains
FCCh. This means the contents of
location FCCh will be added to that
of the W register and stored back in
FCCh.
000h
100h
200h
300h
Bank 0
Bank 1
Bank 2
Bank 3
through
Bank 13
E00h
F00h
FFFh
Bank 14
Bank 15
Data Memory
© 2006 Microchip Technology Inc.
Advance Information
DS39762A-page 89