PIC16C58B-20I/SO Ver la hoja de datos (PDF) - Microchip Technology
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PIC16C58B-20I/SO Datasheet PDF : 192 Pages
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PIC16C5X
6.7 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.
EXAMPLE 6-1: INDIRECT ADDRESSING
• Register file 08 contains the value 10h
• Register file 09 contains the value 0Ah
• Load the value 08 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 = 09h)
• 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).
A simple program to clear RAM locations 10h-1Fh
using indirect addressing is shown in Example 6-2.
EXAMPLE 6-2:
HOW TO CLEAR RAM
USING INDIRECT
ADDRESSING
NEXT
CONTINUE
MOVLW
MOVWF
CLRF
INCF
BTFSC
GOTO
H'10'
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 either a 5-bit (PIC16C54, PIC16CR54,
PIC16C55, PIC16C56, PIC16CR56) or 7-bit
(PIC16C57, PIC16CR57, PIC16C58, PIC16CR58)
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.
PIC16C54, PIC16CR54, PIC16C55, PIC16C56,
PIC16CR56: These do not use banking. FSR<6:5> bits
are unimplemented and read as '1's.
PIC16C57, PIC16CR57, PIC16C58, PIC16CR58:
FSR<6:5> are the bank select bits and are used to
select the bank to be addressed (00 = bank 0,
01 = bank 1, 10 = bank 2, 11 = bank 3).
FIGURE 6-10:
DIRECT/INDIRECT ADDRESSING
Direct Addressing
(FSR)
(opcode)
65
43 2 10
Indirect Addressing
(FSR)
6 543 2 1 0
bank select location select
00
00h
Data
0Fh
Memory(1) 10h
01
10
11
Addresses map back to
addresses in Bank 0.
bank location select
1Fh
3Fh
5Fh
7Fh
Bank 0 Bank 1 Bank 2 Bank 3
Note 1: For register map detail see Section 6.2.
1997-2013 Microchip Technology Inc.
Preliminary
DS30453E-page 33
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