Information Technology Activities: April 2014

LOGIC GATES

AND - True if A and B are both True
OR - True if either A or B are True
NOT - Inverts value: True if input is False; False if input is True
XOR - True if either A or B are True, but False if both are True
NAND - AND followed by NOT: False only if A and B are both True
NOR - OR followed by NOT: True only if A and B are both False
XNOR - XOR followed by NOT: True if A and B are both True or both False

   (http://www.techterms.com/definition/logicgate)

schematic diagram
   - is a representation of the elements of a system using abstract, graphic symbols rather than realistic pictures. A schematic usually omits all details that are not relevant to the information the schematic is intended to convey, and may add unrealistic elements that aid comprehension. (http://en.wikipedia.org/wiki/Schematic)

truth table
      - is a mathematical table used in logic—specifically in connection with Boolean algebra, boolean functions, and propositional calculus—to compute the functional values of logical expressions on each of their functional arguments, that is, on each combination of values taken by their logical variables (Enderton, 2001). (http://en.wikipedia.org/wiki/Truth_table)

Logic Gates with Truth Table

     AND gate

  
The AND gate is an electronic circuit that gives a high output (1) only if all its inputs are high. A dot (.) is used to show the AND operation i.e. A.B. Bear in mind that this dot is sometimes omitted i.e. AB

OR gate

  
The OR gate is an electronic circuit that gives a high output (1) if one or more of its inputs are high. A plus (+) is used to show the OR operation.

NOT gate

  
The 'Exclusive-NOR' gate circuit does the opposite to the EOR gate. It will give a low output if either, but not both, of its two inputs are high. The symbol is an EXOR gate with a small circle on the output. The small circle represents inversion.

(http://www.ee.surrey.ac.uk/Projects/CAL/digital-logic/gatesfunc/index.html)

74 Series Logic IC Datasheets :

part #	description
74LS00	Quad 2-Input NAND Gate
74LS01	Quad 2-Input NAND Gate; Open Collector Outputs
74LS02	Quad 2-Input NOR Gate
74LS03	Quad 2-Input NAND Gate; Open Collector Outputs
74LS04	Hex Inverter
74LS05	Hex Inverter; Open Collector Outputs
74LS06	Hex Inverter; Open Collector High Voltage Outputs
74LS07	Hex Buffer; Open Collector High Voltage Outputs
74LS08	Quad 2-Input AND Gate
74LS09	Quad 2-Input AND Gate; Open Collector Outputs
74LS10	Triple 3-Input NAND Gate
74LS11	Triple 3-Input AND Gate
74LS12	Triple 3-Input NAND Gate; Open Collector Outputs
74LS13	Dual 4-Input NAND Schmitt Triggers
74LS14	Hex Schmitt-Trigger Inverter
74LS15	Triple 3-Input AND Gate; Open Collector Outputs
74LS16	Hex Inverter; Open Collector 15V Outputs
74LS17	Hex Driver; Open Collector 15V Outputs
74LS19	NAND Schmitt Trigger; Totem Pole Output
74LS20	Dual 4-Input NAND Gate
74LS21	Dual 4-Input AND Gate; Open Collector Outputs
74LS22	Dual 4-Input NAND Gate; Open Collector Outputs
74LS23	2x Four input NOR with Strobe
74LS25	2x Four input NOR with Strobe
74LS26	Quad 2-Input NAND Gate; OC (15V)
74LS27	Triple 3-Input NOR Gate
74LS28	Quad 2-Input NOR Gates
74LS30	8-Input NAND Gate
74LS31	Delay Element
74LS32	Quad 2-Input OR Gate
74LS33	Quad 2-Input NOR Gate; Open Collector Outputs
74LS37	Quad 2-Input NAND Gates
74LS38	Quad 2-Input NAND Gates; Open Collector Outputs
74LS39	4x Two input NAND, Open collector
74LS40	Dual 4-Input NAND Gates
74LS42	BCD to DECIMAL Decoder
74LS45	Four-to-Ten (BCD to Decimal) DECODER, High current
74LS46	BCD to Seven-Segment DECODER, Open Collector, lamp test and leading zero handling
74LS47	BCD to 7-Segment Decoder; Open Collector Outputs (15V)
74LS48	BCD to 7-Seg Decoder; Outputs Active high
74LS49	BCD to 7-Seg Decoder-Outputs Active High
74LS50	2x (Two input AND) NOR (Two input AND), expandable
74LS51	Dual AND-OR-INVERT Gates
74LS53	NOR of Four Two input ANDs, expandable
74LS54	4-Wide AND-OR-INVERT Gate
74LS55	4-Wide; 2-Input AND-OR-INVERT Gate
74LS56	Frequency Divider
74LS57	Frequency Divider
74LS64	4-3-2-2 AND-OR-INVERT
74LS65	4-3-2-2 AND-OR-INVERT
74LS68	Dual 4-Bit Decade or Binary Counter
74LS69	Dual 4-Bit Decade or Binary Counter
74LS70	1x gated JK FLIPFLOP with preset and clear
74LS72	1x gated JK FLIPFLOP with preset and clear
74LS73	Dual J-K Flip-Flop
74LS74	Dual D-Type Flip-Flop
74LS75	Dual 2-Bit D-Type Flip-Flop
74LS76	Dual J-K Flip-Flop
74LS77	4-Bit D-Type Latch
74LS78	Dual J-K Flip-Flop
74LS83	4-Bit Full Adder
74LS85	4-Bit Comparator
74LS86	Quad Exclusive OR Gate
74LS90	Decade Counter
74LS91	8-Bit Shift Register
74LS92	Divide-By-12 Counter
74LS93	4-Bit Binary Counter
74LS94	Four bit SHIFT register
74LS95	4-Bit Shift Register with Parallel Inputs and Outputs
74LS96	5-Bit Shift Register with Parallel Inputs and Outputs
74LS107	Dual J-K Master Slave Flip-Flop
74LS109	Dual J-K Flip-Flop
74LS112	Dual J-K Flip-Flop with Preset and Clear
74LS113	Dual J-K Flip-Flop
74LS114	Dual J-K Flip-Flop
74LS116	2x Four bit LATCH with clear
74LS121	Monostable Multivibrator
74LS122	Retriggerable Monostable Multivibrator
74LS123	Retriggerable Monostable Multivibrator
74LS124	2x Clock Generator or Voltage Controlled Oscillator
74LS125	Quad Line Driver; 3-State Outputs
74LS126	Quad Line Driver; 3-State Outputs
74LS128	4x Two input NOR, Line driver
74LS130	Retriggerable Monostable Multivibrator
74LS132	Quad 2-Input NAND Schmitt Trigger
74LS133	13-Input NAND Gate
74LS134	Twelve input NAND, Tri-state
74LS135	4x Two input XOR (exclusive or)
74LS136	Quad 2-Input Exclusive OR Gates
74LS137	3-Line to 8-Line Demultiplexer with Address Latch
74LS138	3-Line to 8-Line Demultiplexer
74LS139	2-Line to 4-Line Decoder/Demultiplexer
74LS140	2x Four input NAND, 50 ohm Line Driver
74LS143	Four bit counter and latch with 7-segment LED driver
74LS145	BCD to Decimal Decoder/Driver
74LS147	10-Line to 4-Line Priority Encoder
74LS148	8-Line to 3-Line Priority Encoder
74LS150	16-1 SELECTOR (multiplexer)
74LS151	8-Line to 1-Line Multiplexer
74LS153	Dual 4-Line to 1-Line Multiplexer
74LS154	4-Bit Binary Decoder/Demultiplexer
74LS155	Dual 2-Bit Binary Decoders/Demultiplexer
74LS156	Dual 2-Bit Binary Decoders/Demultiplexer
74LS157	Quad 2-Line to 1-Line Multiplexer
74LS158	Quad 2-Line to 1-Line Multiplexer
74LS159	4-16 DECODER (demultiplexer), Open collector
74LS160	4-Bit Synchronous Programmable Counter
74LS161	4-Bit Synchronous Programmable Counter
74LS162	4-Bit Synchronous Programmable Counter
74LS163	4-Bit Synchronous Programmable Counter
74LS164	8-Bit Shift Register with Parallel Outputs
74LS165	8-Bit Shift Register with Parallel Inputs
74LS166	8-Bit Shift Register with Parallel Inputs
74LS168	Up/Down 4-Bit Synchronous Counter
74LS169	Up/Down 4-Bit Synchronous Counter
74LS170	16-Bit RAM; Open Collector Outputs
74LS173	4-Bit Quad D-Type Flip-Flops; 3-State Outputs
74LS174	Hex D-Type Flip-Flop
74LS175	Quad D-Type Flip-Flop
74LS180	Four bit parity checker
74LS181	4-bit Arithmetic Logic Unit
74LS182	Look Ahead Carry Generator
74LS183	Dual Carry-Save Full Adder
74LS190	Synchronous Up/Down Decade Counter
74LS191	Synchronous Up/Down 4-Bit Binary Counter
74LS192	Synchronous Up/Down Decade Counter
74LS193	Synchronous Up/Down 4-Bit Binary Counter
74LS194	4-Bit Bidirectional Shift Register
74LS195	4-Bit Parallel-Access Shift Register
74LS196	Programmable Decade Counter
74LS197	Programmable Decade Counter
74LS198	Eight bit parallel in and out bidirectional SHIFT register
74LS199	Eight bit parallel in and out bidirectional SHIFT register, JK serial input
74LS221	Dual Monostable Multivibrator; Schmitt-Trigger Input
74LS240	Octal Inverting Buffer/Transciever; 3-State Outputs
74LS241	Octal Buffer/Transciever; 3-State Outputs
74LS242	Quad 3-State Bus Transceiver
74LS243	4-Bit Bidirectional Bus Driver
74LS244	Octal 3-State Noninverting Buffer
74LS245	Octal 3-State Noninverting Bus Transceiver
74LS247	BCD to 7-Seg Decoder/Display Driver OC (15V)
74LS248	BCD to 7-Seg Decoder/Display Driver OC (15V)
74LS249	BCD to 7-Seg Decoder/Display Driver OC (15V)
74LS251	8-Line to 1-Line Multiplexer; 3-State Outputs
74LS253	Dual 4-Input Data Selecttor/Multiplexer 3-State
74LS256	Dual 4-Bit Addressable Latch
74LS257	Quad 2-Line to 1-Line Multiplexers; 3-State Outputs
74LS258	Quad 2-Line to 1-Line Multiplexers; 3-State Outputs
74LS259	8-Bit Adressable Latch
74LS260	Dual 5-Input NOR Gate
74LS266	Quad Exclusive NOR Gate
74LS269	8-BIT BIDIRECTIONAL BINARY COUNTER
74LS273	Octal D-Type Flip-Flop; Common Clock and Clear
74LS279	Quad SR-Flip-Flops
74LS280	9-Bit Parity checker
74LS283	4-Bit Full Adder
74LS290	4-Bit Decade/Binary Counter
74LS298	Quad 2-Line to 1-Line Multiplexers with Latch
74LS299	8-Bit Bidirectional Universal Shift Register
74LS322	8-Bit Sign-Extend Shift Register
74LS323	8-Bit Universal Shift Register with Latch
74LS348	8-Line to 3-Line Priority Encoder with 3-State Outputs
74LS352	Dual 4-Line to 1-Line Multiplexers
74LS353	Dual 4-Line to 1-Line Multiplexers with 3-State Outputs
74LS365	Hex Bus Line Drivers
74LS366	3-State Hex Line Driver
74LS367	Hex Bus Line Drivers
74LS368	Hex Inverting Bus Line Drivers
74LS373	Octal D-Type Latch
74LS374	Octal D-Type Flip-Flop
74LS375	Quad D-Type Latch
74LS377	Octal D-Type Flip-Flop
74LS378	Hex D-Type Flip-Flop
74LS379	Quad D-Type Flip-Flop
74LS386	Quad 2-Input Exclusive OR Gates
74LS390	Dual Decade Counters
74LS393	Dual Decade Counters
74LS395	4-Bit Shift Register with 3-State Outputs
74LS398	Quad 2-Input Register
74LS399	Quad 2-Input Register
74LS490	Dual Decade Counter
74LS521	8-BIT IDENTITY COMPARATOR
74LS533	Octal D-Type Transparent Latche
74LS534	Octal Invering D-Type Flip-Flop
74LS538	1-OF-8 DECODER WITH 3-STATE OUTPUTS
74LS540	8-Bit Inverting Line Driver
74LS541	OCTAL BUFFER/LINE DRIVER WITH 3-STATE OUTPUTS
74LS543	OCTAL REGISTERED TRANSCEIVER, NON-INVERTING, 3-STATE
74LS544	OCTAL REGISTERED TRANSCEIVER, INVERTING, 3-STATE
74LS568	4-BIT BIDIRECTIONAL COUNTERS (WITH 3-STATE OUTPUTS)
74LS569	4-Bit Synchronous Counter
74LS574	8-Bit D-Type Flip-Flop/Bus Driver
74LS579	8-BIT BIDIRECTIONAL BINARY COUNTER (3-STATE)
74LS620	OCTAL BUS TRANSCEIVER WITH 3-STATE OUTPUTS (INVERTING AND NONINVERTING)
74LS623	Octal Bus Transcievers
74LS629	Voltage Controlled Oscilator
74LS640	Octal Bus Transciever
74LS646	Octal Bus Transciever
74LS648	Octal Bus Transciever/Register
74LS657	OCTAL BIDIRECTIONAL TRANSCEIVER WITH 8-BIT PARITY GENERATOR CHECKER (3-STATE OUTPUTS)
74LS669	4-Bit Synchronous Up/Down Counter
74LS670	4-By-4 Register File; 3-State Outputs
74LS682	8-Bit Magnitude/Identity Comparator
74LS684	8-Bit Magnitude Comparators
74LS688	8-Bit Magnitude Comparators
74LS748	8-Line to 3-Line Priority Encoder
74LS779	8-BIT BIDIRECTIONAL BINARY COUNTER (3-STATE)
74LS795	Octal Buffer with 3-State Outputs
74LS848	8-Line to 3-Line Priority Encoder with 3-State Outputs
74LS2245	25Ohm Octal Bidirectional Transceiver With 3-State Inputs and Outputs
74LS3893	QUAD FUTUREBUS BACKPLANE TRANSCEIVER (3 STATE + OPEN COLLECTOR)

(http://www.skot9000.com/ttl/)

LOGIC GATES and COMBINATION

    logic gates
           - is an idealized or physical device implementing a Boolean function; that is, it performs a logical operation on one or more logical inputs, and produces a single logical output. Depending on the context, the term may refer to an ideal logic gate, one that has for instance zero rise time and unlimited fan-out, or it may refer to a non-ideal physical device .
              Logic circuits include such devices as multiplexers, registers, arithmetic logic units (ALUs), and computer memory, all the way up through complete microprocessors, which may contain more than 100 million gates. In practice, the gates are made from field-effect transistors (FETs), particularly MOSFETs (metal–oxide–semiconductor field-effect transistors).

Combination of Basic Logic Gates

The OR, AND and NOT gates are the three basic circuits that make up all digital circuits. We shall discuss a few combinations of theses basic circuits.

(I) NAND Gate: It is combination of AND gate is connected to the input of a NOT gate as shown in Fig. (a). Clearly, the output of a NAND gate is opposite to the AND gate. This is illustrated in the truth table for the NAND gate. Note that truth table for NAND gate is developed by inverting the output of the AND gate.
The Boolean expression for NAND function is

This Boolean expression can be read as Y = not A . B. TO perform the Boolean algebra operation, First the input must be AND and then the inversion is performed. Note that output from NAND gate is always 1 excepted when all of the input are 1.Fig. (b) shows the logic symbol for a NAND gate. The title bubble (small circle) on the right end of the symbol means to invert the AND.


Fig. (a)		Fig. (b)

Inputs		Outputs
A	B	AND(Y')	NAND(Y)
0	0	0	1
0	1	0	1
1	0	0	1
1	1	1	0

Truth Table of NAND

(II) NOR Gate: It is a combination of OR gate and NOT gate. In other words, output of OR gate is connected to the input of a NOT gate as shown in Fig. (c). Note that output of OR gate is inverted to form NOR gate. This is illustrated in the truth table for NOR gate. It is clear that truth table for NOR gate is developed by inverting the outputs of the OR gate.


Fig. (c)		Fig. (d)

Inputs		Outputs
A	B	OR(Y')	NOR(Y)
0	0	0	1
0	1	1	0
1	0	1	0
1	1	1	0

Truth Table of NOR

The Boolean expression for NOR function is:

The Boolean expression can be read as Y = not A or B. To perform the Boolean algebra operation, first the input must be OR and then inversion is performed. Note that output from a NOR gate is high(1) only when all the inputs are low (0). If any of the inputs are high (1) the output is low (0). fig. (d) shows the logic symbol for a NOR gate. The bubble (small circle) at the Y output indicates inversion.