PIC10F200/202/204/206
EXAMPLE 4-1:
HOW TO CLEAR RAM
USING INDIRECT
ADDRESSING
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.
MOVLW
MOVWF
0x10
;initialize pointer
;to RAM
FSR
NEXT
CLRF
INDF
;clear INDF
;register
INCF
BTFSC
GOTO
FSR,F
FSR,4
NEXT
;inc pointer
;all done?
;NO, clear next
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
CONTINUE
:
:
;YES, continue
• A read of the INDF register will return the value
of 10h
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.
• Increment the value of the FSR register by one
(FSR = 0A)
• A read of the INDR register now will return the
value of 0Ah.
The FSR<4:0> bits are used to select data memory
addresses 00h to 1Fh.
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).
Note:
PIC10F200/202/204/206 – Do not use
banking. FSR <7:5> are unimplemented
and read as ‘1’s.
A simple program to clear RAM locations 10h-1Fh
using indirect addressing is shown in Example 4-1.
FIGURE 4-6:
DIRECT/INDIRECT ADDRESSING (PIC10F200/202/204/206)
Direct Addressing
(opcode) 0
Indirect Addressing
(FSR)
4
0
4
Location Select
Location Select
00h
Data
Memory
0Fh
10h
(1)
1Fh
Bank 0
Note 1: For register map detail, see Section 4.3 “Data Memory Organization”.
© 2007 Microchip Technology Inc.
DS41239D-page 23
MICROCHIP [ MICROCHIP ]
