lecture17 - Page 4 Signed Inequalities b Operands b If...

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CMPT 150 Arithmetic Operations Page 1 Adding and Subtracting b We know how to build a simple adder: FA FA FA FA A 3 B 3 A 2 B 2 A 1 B 1 A 0 B 0 0 C out b Incorporating subtraction: b We want to modify this circuit to add a new input M such that: b M=0: S b A + B b M=1: S b A B b Remember: S b A B = S 3 S 2 S 1 S 0 CMPT 150 Arithmetic Operations Page 2 Four Bit Adder/Subtractor b Note the following: b B 0 = b B 1 = b Note that we lose the ability to add with carry b This means we cannot build an 8-bit adder/subtractor by stringing two 4-bit adder/subtractor’s together FA FA FA FA S 3 S 2 S 1 S 0 C out CMPT 150 Arithmetic Operations Page 3 b We haven’t considered multiply and divide b Real integer units do multiply and divide using an iterative process b Using sequential circuits and multiple cycles b Another possibility is to have a giant look-up table in ROM b Only requires a single cycle b To multiply 2 8-bit numbers requires: b This option is fast, but not cost effective CMPT 150 Arithmetic Operations
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Unformatted text preview: Page 4 Signed Inequalities b Operands b If high-order bit is 0 then the number is positive b If high-order bit is 1 then the number is 2s complement (negative) b Comparisons b If both numbers positive: b If one positive, one negative: b If both numbers negative: CMPT 150 Arithmetic Operations Page 5 Sequential Circuits b A logic circuit is sequential if the current output values depend on past as well as current input values. b Assembled by combining combinational circuits with memory emory elements are called ip ops b Memory elements are called flip-flops b Initial attempts at building a flip-flop: x y x Problem: CMPT 150 Arithmetic Operations Page 6 SR Latch b If S=0 and R=0 b b If S=1 and R=0 b S x b b If S=0 and R=1 b b b If S=1 and R=1 b b b R Q S R Q(t+1) 0 0 0 1 1 0 1 1 Characteristic Table...
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This note was uploaded on 04/27/2011 for the course CMPT 150 taught by Professor Dr.anthonydixon during the Spring '08 term at Simon Fraser.

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lecture17 - Page 4 Signed Inequalities b Operands b If...

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