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**Boolean Algebra Variables: only 2 values (0,1)**

Huntington’s (1804) axioms: 1 1 = = 0 a 0 = a + 1 = 1 a a’ = a + a’ = 1 a b = b a a + b = b + a a(b+c)=ab+ac a+bc=(a+b)(a+c) Verification by truth table: abc (a+b)c ac+bc Application to electric switches (open - 0, closed - 1): a L c 220V~ b L = (a + b)c = ac + bc a c L 220V~ b c L = ac + bc Every logical function can be specified by truth table and implemented as sum of product form,e.g. L = a’bc + ab’c + abc.

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**Combinational Circuits**

Output is direct function of inputs a a’ NOT Switch light L implemented by gates L = a’bc + ab’c + abc sum of products. a b a+b a b c L OR a b ab Function presentation by Karnough map every product term has a field, and neighboring fields differ by only one variable. Example (three input variables): L = abc + ab’c + a’bc = abc + ab’c + abc + a’bc = ac(b + b’) + bc(a + a’) = ac + bc = (a + b)c b a 1 1 c a a+b 1 b L c L

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**Decoders and Multiplexers**

Decoder has n inputs and 2n outputs: A B BA Mux determines which input will connect to output: A B C D A B C D 1 1 1 1 S[1:0] 2 S 1 OUT OUT

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**Binary Adder Design a0 a3 a2 a1 b3 b2 b1 b0 c3 c2 c1 c0 c4 s3 s2 s1 s0**

co ci a b ci s co Truth Table a b ci s co Karnough maps a b ci a b ci 1 1 1 1 1 1 1 1 s = ab ci +ab ci’ +a’b’ ci +a’b’ ci’= (ab + a’b’)ci + (ab + a’b’)ci’ = (a + b’) + ci = a + b’ + ci co = ab + aci + bci

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**Programmable Logic Arrays PLA**

Any logical function can be implemented by two levels circuits: ANDs and ORs. A B C X Y

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**Design of the RS flip-flop**

c b a p x 1 a: a: b: b: a b CC p c a b p stable x c b a x 1 p = a + b’c b’ p c a a b p’ a b p p time

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**Registers One bit register = memory cell WE = Clock pulse in bit gate**

out bit Eight bit register b7 b6 b5 b4 b3 b2 b1 b0 WE

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**The Concept of Memory WE N address lines (bus) address space = 2N**

Memory as array of registers: address space and addressability address decoder memory 0 WE memory 1 memory 2 N address lines (bus) address space = 2N memory 3 memory 4 memory 5 memory 6 memory 7 M data lines (bus)

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**Memory details address word select word WE input bits write enable**

Decoder asserts one of the word select lines, based on address. Word select activates one of the output AND gates, which drives the selected data to the output OR gate. (For a read, this is basically a MUX -- decoder ANDed with signals, results ORed together.) When writing, the only WE bits for the proper word are asserted (based on decoder again). output bits

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**Design of the JK flip-flop**

master slave J A B Q Q’ A B K CL B closes A closes A opens master accepts B opens slave accepts At no time the path between inputs JK and outputs QQ’ is closed.

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**Synchronous Sequential Circuit**

Output Input CC Next state Present state A B clock * Output is a function of Input and Present state. * Next state is a function of Input and Present state. * Present state is delayed Next state.

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**Traffic warning sign All off 1,2 on 00 01 10 11 0,1 1 1 2 3 4 5**

1,2,3,4 00 01 10 11 0,1 1 1,2 1 2 3 4 5 SW SW 3,4 Combinational Circuit 5 SW E1 E1+ E2 E2+ State SW current next output SW E1 E2 E1+ E2+ 1,2 3,4 5 Cl E1 E2 1,2 3,4 5 E1+ E2+ E1 E2 SW E1+ = SW E1’ E2 + SW E1 E2’ E2+ = SW E1’ E2’ + SW E1 E2’ 1,2 = E SW E1 E2 3,4 = E SW E1 E2 5 = SW E1 E2 Combinational Circuit

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**Reversible counter modulo 5**

000 110 010 011 001 1 a b c Next State 1 x a b c I 1 x a b c I 1 x a b c I a+ = a’bc’I’ + b’c’I b+ = (c + a’b) I’ + c’I c+ = ab’ + b’I’ + a’b I a+ = a’bc’I’ + b’c’I b+ = (c + a’b) I’ + c’I c+ = ab’ + b’I’ + a’b I a+ b+ c+ a b c I CL

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CS1104 – Computer Organization

CS1104 – Computer Organization

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