PIC16C621A Microchip Technology Inc., PIC16C621A Datasheet - Page 26

• Manufacturer Part Number: PIC16C621A
• Description: Eprom-based 8-bit Cmos Microcontrollers
• Manufacturer: Microchip Technology Inc.

PIC16C62X
4.4
The INDF register is not a physical register. Addressing
the INDF register will cause indirect addressing.
Indirect addressing is possible by using the INDF
register. Any instruction using the INDF register
actually accesses data pointed to by the File 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 4-9. However, IRP
is not used in the PIC16C62X.
A simple program to clear RAM location 20h-7Fh using
indirect addressing is shown in Example 4-1.
FIGURE 4-9:
DS30235J-page 24
RP1
bank select
RP0
Note 1: The RP1 and IRP bits are reserved; always maintain these bits clear.
For memory map detail see (Figure 4-4, Figure 4-5, Figure 4-6 and Figure 4-7).
Indirect Addressing, INDF and
FSR Registers
(1)
location select
6
Direct Addressing
Data
Memory
DIRECT/INDIRECT ADDRESSING PIC16C62X
from opcode
7Fh
00h
Bank 0
00
0
Bank 1
01
Bank 2
10
not used
EXAMPLE 4-1:
NEXT clrf
CONTINUE:
Bank 3
11
movlw
movwf
incf
btfss
goto
IRP
bank select
180h
1FFh
(1)
0x20
FSR
INDF
FSR
FSR,7
NEXT
7
Indirect Addressing
INDIRECT ADDRESSING
 2003 Microchip Technology Inc.
;initialize pointer
;to RAM
;clear INDF register
;inc pointer
;all done?
;no clear next
;yes continue
FSR register
location select
0