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When running a program,
the CPU firsts loads an
instruction.
It then processes data
using this instruction.
Addressing modes tell
the CPU where to find
the data.
The 6502 has several
addressing modes.
A sample is given below.
IMMEDIATE addressing.
In the program, the data
follows the instruction.
ADD 99
Add 99 to the contents
of the accumulator.
ABSOLUTE addressing.
In the program, the 16
bit address of the data
follows the instruction.
STA 1243
Store the contents of
the accumulator at
address 1243.
ZERO PAGE addressing.
In the program, the
instruction is followed
by an 8 bit address.
This means that only
addresses 0-255 (in page
zero) can be used.
CMP 230
Compare the contents of
the accumulator with the
contents of address
0230.
Other addressing modes
are
IMPLIED
RELATIVE
ACCUMULATOR
INDEXED
INDIRECT
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