Overview Logic Combinational Logic Sequential Logic Storage Devices SR FlipFlops D Flip Flops JK...
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Transcript of Overview Logic Combinational Logic Sequential Logic Storage Devices SR FlipFlops D Flip Flops JK...
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 Overview Logic Combinational Logic Sequential Logic Storage Devices SR FlipFlops D Flip Flops JK Flip Flops Registers Addressing Computer Memory
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 Logical Completeness Can implement ANY truth table with AND, OR, NOT. ABCD 0000 0010 0101 0110 1000 1011 1100 1110 1. AND combinations that yield a "1" in the truth table. 2. OR the results of the AND gates.
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 Combinational vs. Sequential Combinational Circuit always gives the same output for a given set of inputs ex: adder always generates sum and carry, regardless of previous inputs Sequential Circuit stores information output depends on stored information (state) plus input so a given input might produce different outputs, depending on the stored information example: ticket counter advances when you push the button output depends on previous state useful for building memory elements and state machines
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 RS : Simple Storage Element R is used to reset or clear the element set it to zero. S is used to set the element set it to one. If both R and S are one, out could be either zero or one. quiescent state  holds its previous value note: if a is 1, b is 0, and vice versa Out is usually called Q, and the other output call Q 1 0 1 1 1 1 0 0 1 1 0 0 1 1
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 Clearing the RS Suppose we start with output = 1, then change R to zero. Output changes to zero. Then set R=1 to store value in quiescent state. 1 0 1 1 1 1 0 0 1 0 1 0 0 0 1 1
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 Setting the RS Suppose we start with output = 0, then change S to zero. Output changes to one. Then set S=1 to store value in quiescent state. 1 1 0 0 1 1 0 1 1 1 0 0
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 Basic SR Flip Flop Nor Gates: Nand Gates:
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 Clocked SR Flip Flop
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 D Flip Flop (D Latch)
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 DLatch Two inputs: D (data) and WE (write enable) when WE = 1, latch is set to value of D S = NOT(D), R = D when WE = 0, latch holds previous value S = R = 1
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 Trigger Flip Flop
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 Master Slave Flip Flop
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 MasterSlave DLatch Flip flop A pair of gated Dlatches, to isolate next state from current state. During 1 st phase (clock=1), previouslycomputed state becomes current state and is sent to the logic circuit. During 2 nd phase (clock=0), next state, computed by logic circuit, is stored in Latch A.
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 Positive Edge Triggered Flip Flop
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 JK Flip Flop
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 JK as a Universal Flip Flop JK as an SR use set and pre inputs JK as a Toggle connect J and K JK as a D connect NOT J to K
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 Logic Spec Sheets Texas Instruments: http://www.ti.com/hdr_p_logic UW: http://www.ee.washington.edu/stores/
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 Register A register stores a multibit value. We use a collection of Dlatches, all controlled by a common WE. When WE=1, nbit value D is written to register.
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 Recall: Representing Multibit Values Number bits from right (0) to left (n1) just a convention  could be left to right, but must be consistent Use brackets to denote range: D[l:r] denotes bit l to bit r, from left to right May also see A, especially in hardware block diagrams. A = 0101001101010101 A[2:0] = 101 A[14:9] = 101001 0 15
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 Memory Now that we know how to store bits, we can build a memory a logical k m array of stored bits. k = 2 n locations m bits Address Space: number of locations (usually a power of 2) Addressability: (Word Length) number of bits per location (e.g., byteaddressable)
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 1K X 4 SRAM (Part Number 2114N)
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 Memory Design 1K x 4 A[00:09] D[03:00] Addr Block Select
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 Memory Design 1K x 8 A[00:09] D[07:04] A[00:09] D[03:00] Addr Block Select => D[07:04] D[03:00]
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 Memory Design  2k x 8 D[07:04] D[03:00] Block 00 Block 01
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 Memory Design  4k x 8 D[07:04] D[03:00] Block 00 Block 01 Block 10 Block 11
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 2 2 x 3 Memory address decoder word selectword WE address write enable input bits output bits
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 More Memory Details Two basic kinds of RAM (Random Access Memory) Static RAM (SRAM) fast, maintains data as long as power applied Dynamic RAM (DRAM) slower but denser, bit storage decays must be periodically refreshed Also, nonvolatile memories: ROM, PROM, flash,