l4_seqntl_blocks

111 spring 2004 introductory digital systems

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Unformatted text preview: 004 Introductory Digital Systems Laboratory 2 A Sequential System System Sequential circuits have memory (i.e., remember the past) The current state is "held" in memory and the next state is computed based the current state and the current inputs In a synchronous systems, the clock signal orchestrates the sequence of events L4: 6.111 Spring 2004 Introductory Digital Systems Laboratory 3 A Simple Example Example Adding N inputs (N-1 Adders) in0 in1 in2 inN-1 Using a sequential (serial) approach reset in DQ clk Current_Sum L4: 6.111 Spring 2004 Introductory Digital Systems Laboratory 4 Implementing State: Bi-stability stability Vo1 = Vi2 Vi2 = Vo1 Vo2 = Vi1 Point C is Metastable C V o1 Vi2 G V i2 = V o 1 Vi1 = V o2 A V i1 A V i 2 = V o1 C V o2 Points A and B are stable (represent 0 & 1) B V i 1 = V o2 L4: 6.111 Spring 2004 Introductory Digital Systems Laboratory B G V i1 = V o2 5 NOR-based Set-Reset (SR) Flipflop Flipflop S R S Q Q S 0 Q 1 0 1 R 0 0 1 1 Q Q 1 0 0 Q Q 0 1 0 QQ 01 SR = 0 1 SR = 0 1 SR = 1 0 SR = 00, 01 SR = 1 0 SR = 00, 10 QQ 10 SR = 11 SR = 1 1 QQ 00 SR = 1 1 R Reset Q Forbidden State SR = 0 0 SR = 0 0 Hold Set Reset Set R S Q Q ?? Flip-flop refers to a bi-stable element (edge-tr...
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