Filter
Top Products
SUPPLEMENT
Addressing Modes
The address that the
CPU
provides on the
address lines selects
one specific memory or
I/O
device from all those available. This
address can be generated in different ways
depending on the operation being performed.
For
an
instruction fetch, the address comes
from the
CPU
program counter register.
While executing
an
instruction, this address
can be generated many different ways, called
addressing modes.
In the simplest addressing mode, the desired
data
item
is
contained within the instruction
being executed.
In a more complex address-
ing mode the instruction contains the mem-
ory address
of
the data. Or, the instruction
may reference a
CPU register that contains
the memory address
of
the data.
8-5
And finally within some microprocessors, the
instruction may instruct the control circuitry
to
generate a complex address that
is
the sum
of
several address components such as multi-
ple registers plus data contained in the
instruction itself.
Generally, the
most
powerful
micropro-
cessors are the ones with the widest variety
of
addressing
modes
available
to
the
programmer.
When you
put
it all together: the microcom-
puter bus structure, the
CPU registers, the
addressing modes, and the instructions them-
selves, you have the total microcomputer
architecture. The many available microcom-
puters have many different architectures
from which the system designer has to choose
in
selecting
a
microcomputer
for
this
application.