PIC16C62X
4.4
Indirect Addressing, INDF and FSR
Registers
EXAMPLE 4-1:
movlw
NEXT
movwf
clrf
incf
btfss
goto
CONTINUE:
INDIRECT ADDRESSING
0x20
FSR
INDF
FSR
FSR,4
NEXT
;initialize pointer
;to RAM
;clear INDF register
;inc pointer
;all done?
;no clear next
;yes continue
The INDF register is not a physical register. Addressing
the INDF register will cause indirect addressing.
Indirect addressing is possible by using the INDF reg-
ister. Any instruction using the INDF register actually
accesses data pointed to by the 铿乴e select register
(FSR). Reading INDF itself indirectly will produce 00h.
Writing to the INDF register indirectly results in a
no-operation (although status bits may be affected). An
effective 9-bit address is obtained by concatenating the
8-bit FSR register and the IRP bit (STATUS<7>), as
shown in Figure 4-15. However, IRP is not used in the
PIC16C62X.
A simple program to clear RAM location 20h-2Fh using
indirect addressing is shown in Example 4-1.
FIGURE 4-15: DIRECT/INDIRECT ADDRESSING PIC16C62X
Direct Addressing
(1)
RP1
Indirect Addressing
0
IRP
(1)
7
FSR register
0
RP0
6
from opcode
bank select
location select
00
00h
01
10
11
bank select
180h
location select
not used
Data
Memory
7Fh
1FFh
Bank 0
Bank 1
Bank 2
Bank 3
For memory map detail see (Figure 4-4, Figure 4-5, Figure 4-6 and Figure 4-7).
Note 1: The RP1 and IRP bits are reserved, always maintain these bits clear.
DS30235G-page 24
Preliminary
漏
1998 Microchip Technology Inc.