Datasheet

PIC16F716
DS41206B-page 18 © 2007 Microchip Technology Inc.
2.5 Indirect Addressing, INDF and
FSR Registers
The INDF register is not a physical register. Addressing
INDF actually addresses the register whose address is
contained in the FSR register (FSR is a pointer). This is
indirect addressing.
EXAMPLE 2-1: INDIRECT ADDRESSING
• Register file 05 contains the value 10h
• Register file 06 contains the value 0Ah
• Load the value 05 into the FSR register
• A read of the INDF register will return the value of
10h
• Increment the value of the FSR register by one
(FSR = 06)
• A read of the INDR register now will return the
value of 0Ah.
Reading INDF itself indirectly (FSR = 0) will produce
00h. Writing to the INDF register indirectly results in a
no-operation (although Status bits may be affected).
A simple program to clear RAM locations 20h-2Fh
using indirect addressing is shown in Example 2-2.
EXAMPLE 2-2: HOW TO CLEAR RAM
USING INDIRECT
ADDRESSING
An effective 9-bit address is obtained by concatenating
the 8-bit FSR register and the IRP bit of the STATUS
register, as shown in Figure 2-4. However, IRP is not
used in the PIC16F716.
FIGURE 2-4: DIRECT/INDIRECT ADDRESSING
MOVLW 0x20 ;initialize pointer
MOVWF FSR ;to RAM
NEXT CLRF INDF ;clear RAM & FSR
INCF FSR ;inc pointer
BTFSS FSR,4 ;all done?
GOTO NEXT ;no, clear next
CONTINUE
: ;yes, continue
Note 1: For register file map detail see Figure 2-2.
2: Maintain clear for upward compatibility with future products.
3: Not implemented.
Data
Memory
(1)
Indirect AddressingDirect Addressing
bank select location select
RP1:
RP0 6
0
from opcode
IRP FSR register
7
0
bank select
location select
00 01 10 11
Bank 0 Bank 1 Bank 2 Bank 3
FFh
80h
7Fh
00h
17Fh
100h
1FFh
180h
(3) (3)
(2)
(2)