Datasheet

© 2007 Microchip Technology Inc. DS41239D-page 23
PIC10F200/202/204/206
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.
4.10 Indirect Addressing
• Register file 09 contains the value 10h
• Register file 0A contains the value 0Ah
• Load the value 09 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 = 0A)
• 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
The FSR is a 5-bit wide register. It is used in conjunc-
tion 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.
FIGURE 4-6: DIRECT/INDIRECT ADDRESSING (PIC10F200/202/204/206)
Note: PIC10F200/202/204/206 – Do not use
banking. FSR <7:5> are unimplemented
and read as ‘1’s.
MOVLW 0x10 ;initialize pointer
MOVWF FSR ;to RAM
NEXT CLRF INDF ;clear INDF
;register
INCF FSR,F ;inc pointer
BTFSC FSR,4 ;all done?
GOTO NEXT ;NO, clear next
CONTINUE
: ;YES, continue
:
Note 1: For register map detail, see Section 4.3 “Data Memory Organization”.
Location Select
Location Select
Indirect Addressing
Direct Addressing
Data
Memory
(1)
0Fh
10h
Bank 0
0
4
(FSR)
00h
1Fh
(opcode) 04