PIC18F25K80 MICROCHIP [Microchip Technology], PIC18F25K80 Datasheet - Page 130

• Manufacturer Part Number: PIC18F25K80
• Manufacturer: MICROCHIP [Microchip Technology]

PIC18F66K80 FAMILY
6.4.3.2
In addition to the INDF operand, each FSR register pair
also has four additional indirect operands. Like INDF,
these are “virtual” registers that cannot be indirectly
read or written to. Accessing these registers actually
accesses the associated FSR register pair, but also
performs a specific action on its stored value.
These operands are:
• POSTDEC – Accesses the FSR value, then
• POSTINC – Accesses the FSR value, then
• PREINC – Increments the FSR value by ‘ 1 ’, then
• PLUSW – Adds the signed value of the W register
In this context, accessing an INDF register uses the
value in the FSR registers without changing them.
Similarly, accessing a PLUSW register gives the FSR
value, offset by the value in the W register, with neither
value actually changed in the operation. Accessing the
other virtual registers changes the value of the FSR
registers.
Operations on the FSRs with POSTDEC, POSTINC
and PREINC affect the entire register pair. Rollovers of
the FSRnL register, from FFh to 00h, carry over to the
FSRnH register. On the other hand, results of these
operations do not change the value of any flags in the
STATUS register (for example, Z, N and OV bits).
DS39977C-page 130
automatically decrements it by ‘ 1 ’ afterwards
automatically increments it by ‘ 1 ’ afterwards
uses it in the operation
(range of -127 to 128) to that of the FSR and uses
the new value in the operation
FSR Registers and POSTINC,
POSTDEC, PREINC and PLUSW
Preliminary
The PLUSW register can be used to implement a form
of Indexed Addressing in the data memory space. By
manipulating the value in the W register, users can
reach addresses that are fixed offsets from pointer
addresses. In some applications, this can be used to
implement some powerful program control structure,
such as software stacks, inside of data memory.
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