PIC16C84 Microchip Technology, PIC16C84 Datasheet - Page 18

• Manufacturer Part Number: PIC16C84
• Description: 8 BIT CMOS EEPROM MICROCONTROLLERS
• Manufacturer: Microchip Technology

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PIC16C84
4.5
The INDF register is not a physical register. Address-
ing INDF actually addresses the register whose
address is contained in the FSR register (FSR is a
pointer ). This is indirect addressing.
EXAMPLE 4-1:
• Register file 05 contains the value 10h
• Register file 06 contains the value 0Ah
• Load the value 05 into the FSR register
• A read of the INDF register will return the value of
• Increment the value of the FSR register by one
• A read of the INDF register now will return the
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).
FIGURE 4-7:
DS30445C-page 18
bank select
10h
(FSR = 06)
value of 0Ah.
RP1 RP0
Indirect Addressing; INDF and FSR
Registers
location select
6
DIRECT/INDIRECT ADDRESSING
Data
Memory
INDIRECT ADDRESSING
Direct Addressing
from opcode
00h
0Bh
0Ch
2Fh
30h
7Fh
Bank 0
00
0
Addresses
map back
to Bank 0
Bank 1
01
not used
Bank 2
10
EXAMPLE 4-2:
NEXT
CONTINUE
An effective 9-bit address is obtained by concatenating
the 8-bit FSR register and the IRP bit (STATUS<7>), as
shown in Figure 4-7. However, IRP is not used in the
PIC16C84.
A simple program to clear RAM locations 20h-2Fh
using indirect addressing is shown in Example 4-2.
not used
Bank 3
11
IRP
bank select
movlw
movwf
clrf
incf
btfss
goto
:
00h
7Fh
HOW TO CLEAR RAM
USING INDIRECT
ADDRESSING
7
0x20
FSR
INDF
FSR
FSR,4 ;all done?
NEXT
Indirect Addressing
1997 Microchip Technology Inc.
;initialize pointer
;
;clear INDF register
;inc pointer
;NO, clear next
;YES, continue
(FSR)
to RAM
location select
0