# Arithmetic Logic Unit

**Topics:**Arithmetic logic unit, Computer arithmetic, Bitwise operation

**Pages:**5 (927 words)

**Published:**May 1, 2013

Submitted By,

M.GOVINDHASAMY.

K.GOWTHAM. K.A.GOWTHAMRAJ.

ARITHMETIC LOGIC UNIT

AIM:

To verify the Function table of 4 bit ALU.

APPARATUS REQUIRED:

IC 74181.

* Trainer kit(+5v).

* Connecting probes.

PROCEDURE:

* Connections are made as shown in the Circuit diagram.

* Change the values of the inputs and verify at least 5 functions * given in the function table.

PIN DETAIL & FUNCTION TABLE:-

IC 74181

EXAMPLES:

TRUTH TABLE1:

Kit input| Chip input|

A| B| A| B|

0| 0| 1| 1|

0| 1| 1| 0|

1| 0| 0| 1|

1| 1| 0| 0|

Select lines 0 0 0 0 → A

EQU1: A.A=A

A→0→0→1

Select lines 0 0 0 1 → AB

EQU2: AB→A+B→A+B

0+0=0=1

0+1=1=0

1+0=1=0

1+1=1=0

Select lines 0 1 0 0 → A⊕B

EQU3: A⊕B → A.B+A.B→A.B+A.B

0.0+1.1=1=0 0.1+1.0=0=1 1.0+0.1=0=1 1.1+0.0=1=0 CARRY=LOW MODE=HIGH

TRUTH TABLE2:

Kit input| Chip input|

A| B| A| B|

0| 0| 1| 1|

0| 1| 1| 0|

1| 0| 0| 1|

1| 1| 0| 0|

Select lines 0 0 0 0 → A

EQU1:

A→1→1→0

Select lines 0 1 0 0 → AB

EQU2: AB→A+B

1+1=1

1+0=1

0+1=1

0+0=0

TRUTH TABLE3:

Select lines 0 1 0 0 → A⊕B

EQU3: A⊕B → A.B+A.B→A.B+A.B

0.0+1.1=1=0 0.1+1.0=0=1 1.0+0.1=0=1 1.1+0.0=1=0

CARRY=HIGH MODE=HIGH

TRUTH TABLE 1:

TRUTH TABLE 2:

BLOCK DIAGRAM:

FEATURES:

* Full carry look-ahead for high-speed arithmetic operation on long words. * Provides 16 arithmetic operations: add, subtract, compare, double, plus 12 others. * Provides all 16 logic operations of two variables: EXCLUSIVE-OR, compare, AND, NAND, NOR, OR plus 10 other logic operations. * Output capability: standard, A=B open drain.

WORKING PRINCIPLE:

The 74HC/HCT181 are high-speed Si-gate CMOS devices and are pin compatible with low power Schottky TTL (LSTTL). They are specified in compliance with JEDEC standard no. 7A. The 74HC/HCT181 are 4-bit high-speed parallel Arithmetic Logic Units (ALU). Controlled by the four function select inputs (S0 to S3) and the mode control input (M), they can perform all the 16 possible logic operations or 16 different arithmetic operations on active HIGH or active LOW operands (see function table). When the mode control input (M) is HIGH, all internal carries are inhibited and the device3 performs logic operations on the individual bits as listed. When M is LOW, the carries are enabled and the “181” performs arithmetic operations on the two 4-bit words. The “181” incorporates...

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