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TTL-series 74181 ALU circuitDescriptionThis circuit shows the actual implementation of the
TTL-series 4-bit 74181 ALU integrated circuit.
The input signals for the A and B data inputs pass through
three main stages of logic.
The first stage consists of four identical blocks of logic
connected to one pair of the (A,B) inputs and the four
function selection inputs.
Each block calculates the logical function selected by the S inputs
and generates two output signals which are then passed to the
next stage of logic.
Note that the outputs generated by the first stage of logic
are directly passed through to the F outputs
(via the XOR gates) when the M input is high.
The next stage of logic realizes the carry-look-ahead calculation
for the arithmetic adder functions (when M is low),
while the XOR gates calculate the summation (Ai+Bi) of each pair
of data inputs.
The final stage of logic consists of the output XOR gates
and calculates the final sum by adding the carry bits and
the (Ai+Bi) bits.
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Impressum | 24.11.06