Arithmetic Logic Unit Video Lecture | Digital Electronics - Electrical Engineering (EE)

a computer stores information and it's
registers and RAM and manipulates
information through a variety of means
the component that is responsible for
our bulk these operations is called the
arithmetic logic unit or ALU as its name
implies the ALU performs both arithmetic
and logic operations in this lecture we
focus on describing the general
functionality of a simple ALU ill-used
vary between architectures so this micro
lecture is intended only to deduce the
basic concept of an ALU a computer's
registers each store the same number of
bits when we want to make it what is
stored in these registers the register
file will be instructed to send the
contents of two registers to the ALU in
this example the registers are 8 bits in
length the ALU will perform a
calculation on these two values and send
the result back to the register file to
be stored we tell the a of you what
instruction to perform by sending in a
set of control bits that encode a
message or what operation to perform
because the ALU is a combinational
circuit it will perform these
calculations immediately simplify the
diagram we will use a bus notation where
we group sets of wires together and
indicate how many wires and that group
rather than draw three sets of eight
wires will simply draw three buses a
nail you can perform whatever arithmetic
operations that we know how to implement
such as addition subtraction
multiplication as well as decrement and
increment operations bit ways logical
operators such as not and or and others
comprise a list of non arithmetic
operations such as value comparisons and
setting a registers contents to zero the
details of these operations are covered
in another lecture
suppose that we have an ALU that
receives two control bits because there
are two control bits we can encode four
operations for the ALU to perform I've
chosen two arithmetic operations and two
logic operations for this example the
ALU receives inputs from two 8-bit
registers and sends out eight bits of
information back to the register file
based on the data from the control bits
the ALU knows which operation to perform
in this situation the ALU calculates the
sum and sends it to the register file if
we change the control bits will change
which operation is performed because
this operation does not need an input
from B the B inputs will be ignored the
ALU will send an increment value of a
back to the register file to briefly
introduce the logic operations we'll
examine one of the simpler operations
such as the not operation the not
operation receives only one set of
inputs so again the ALU will ignore the
inputs from B the not operation changes
all zeros to ones and all ones to zeros
the not operation is applied to each bit
in the register individually otherwise
called a bitwise operation finally if we
change the control bits again the ALU
will perform a clear operation which
means that we will set the contents of a
register to zero for this operation the
ALU ignores both inputs and simply sends
out the value 0 notice that the a leo is
sending out 8 zeros because all numbers
even zero are encoded with the same
number of bits in a computer in this
lecture
you saw that an ALU
seized information from the register
file and then performs operations on
this information the control bets encode
information about what operation the ale
used to perform these operations will
either be arithmetic operations or
bitwise logic operations