PIC16F8X_13 Datasheet, PDF (19/128 Pages) Microchip Technology – 18-pin Flash/EEPROM 8-Bit Microcontrollers

PIC16F8X
4.5 Indirect Addressing; INDF and FSR
Registers
The INDF register is not a physical register. Address-
ing INDF actually addresses the register whose
address is contained in the FSR register (FSR is a
pointer). This is indirect addressing.
EXAMPLE 4-1: 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 INDF 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).
FIGURE 4-1: DIRECT/INDIRECT ADDRESSING
RP1 RP0
Direct Addressing
6
from opcode
0
A simple program to clear RAM locations 20h-2Fh
using indirect addressing is shown in Example 4-2.
EXAMPLE 4-2: HOW TO CLEAR RAM
USING INDIRECT
ADDRESSING
NEXT
CONTINUE
movlw
movwf
clrf
incf
btfss
goto
:
0x20 ;initialize pointer
FSR ; to RAM
INDF ;clear INDF register
FSR ;inc pointer
FSR,4 ;all done?
NEXT ;NO, clear next
;YES, continue
An effective 9-bit address is obtained by concatenating
the 8-bit FSR register and the IRP bit (STATUS<7>), as
shown in Figure 4-1. However, IRP is not used in the
PIC16F8X.
Indirect Addressing
IRP
7
(FSR)
0
bank select location select
bank select
00h
0Bh
0Ch
Data
Memory ⁽³⁾
2Fh ⁽¹⁾
30h ⁽¹⁾
4Fh ⁽²⁾
50h ⁽²⁾
00
01
10
11
00h
not used not used
Addresses
map back
to Bank 0
7Fh
7Fh
Bank 0 Bank 1 Bank 2 Bank 3
Note 1: PIC16F83 and PIC16CR83 devices.
2: PIC16F84 and PIC16CR84 devices
3: For memory map detail see Figure 4-1.
location select
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DS30430D-page 19