Arithmetic Logic Unit/function GeneratorThe 74HC181 is a high speed CMOS ARITHMETIC
Logic UNIT/FUNCTION GENERATOR fabricated
with silicon Gate C2
MOS technology. It has the same
highspeed performance ofLSTTL combined withtrue
CMOS low power consumption. These circuits per
form 16 binary arithmetic operations on two 4bit
words as shown in tables 1 and 2. These operations
are selected by the four functionselect lines (S0, S1,
S2, S3) andinclude addition, subtraction, decrement,
and straight transfer. When performing arithmetic
manipulations, theinternal carriesmust be enabled by
applying a lowlevel voltage to themode control input
(M). Afull carry lookahead scheme ismade available
in these devices for fast, simultaneous carry gener
ation by means of two cascadeoutputs (pins 15 and
17) for thefourbits in the package. Whenused in con
junction with theM54HC182 or M74HC182, full carry
lookahead circuits, highspeed arithmetic operations
CAN be performed. These circuits will accomodate ac
tivehigh oractivelow data, if the pin designations are
interpreted as shown below. Subtraction is accom
plished by 1,s complement addition where the 1s
complement of thesubtrahend is generated internally.
The resultant output is 1B1, which requires an end
around or forced carry to produce AB. The 181 CAN
also be utilized as a Comparator The A = B output is
internally decoded from the function outputs (F0, F1,
F2, F3) so that when two words of equal magnitude
are applied at the Aand Binputs, itwill assume a high
level to indicated equality (A = B). The ALUshould be By STMicroelectronics


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