PIC12F508_09 Datasheet, PDF (28/110 Pages) Microchip Technology – 8/14-Pin, 8-Bit Flash Microcontrollers

PIC12F508/509/16F505
4.9 Indirect Data 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.
4.9.1 INDIRECT ADDRESSING
• Register file 07 contains the value 10h
• Register file 08 contains the value 0Ah
• Load the value 07 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 = 08)
• 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 10h-1Fh
using indirect addressing is shown in Example 4-1.
EXAMPLE 4-1:
HOW TO CLEAR RAM
USING INDIRECT
ADDRESSING
NEXT
MOVLW
MOVWF
CLRF
INCF
BTFSC
GOTO
CONTINUE
:
:
0x10
FSR
INDF
FSR,F
FSR,4
NEXT
;initialize pointer
;to RAM
;clear INDF
;register
;inc pointer
;all done?
;NO, clear next
;YES, continue
The FSR is a 5-bit wide register. It is used in conjunction
with the INDF register to indirectly address the data
memory area.
The FSR<4:0> bits are used to select data memory
addresses 00h to 1Fh.
PIC12F508 – Does not use banking. FSR <7:5> are
unimplemented and read as ‘1’s.
PIC12F509 – Uses FSR<5>. Selects between bank 0
and bank 1. FSR<7:6> are unimplemented, read as
‘1’.
PIC16F505 – Uses FSR<6:5>. Selects from bank 0 to
bank 3. FSR<7> is unimplemented, read as ‘1’.
FIGURE 4-7:
DIRECT/INDIRECT ADDRESSING (PIC12F508/509)
Direct Addressing
(FSR)
65
4 (opcode) 0
Indirect Addressing
6 5 4 (FSR) 0
Bank Select Location Select
00
00h
Data
0Fh
Memory⁽¹⁾ _10h
01
Addresses
map back to
addresses
in Bank 0.
Bank Location Select
1Fh
3Fh
Bank 0 Bank 1⁽²⁾
Note 1: For register map detail, see Section 4.3 “Data Memory Organization”.
2: PIC12F509.
DS41236E-page 28
© 2009 Microchip Technology Inc.