# Verilog hdl – II

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MoORE MACHINE revisited A good way to specify Moore is to use separate procedural blocks for Next State Combinational Logic For the state update Sequential Logic Output Combinational Logic

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Verilog hdl II MoORE MACHINE revisited
A good way to specify Moore is to use separate procedural blocks for Next State Combinational Logic For the state update Sequential Logic Output Combinational Logic The three states of moore: Moore DUAL SEQUENCE Overlapping:
A Moore type sequence FSM that reads a binary sequence w and sets z =1if either a 110 or a 101 pattern with overlaps is detected. The state diagram for such a machine is as follows. VERILOG FOR Moore 1mODEL: Verilog Code for MOORE 2: Verilog code for moore 3: Cannot put z in the always block else it would have been edge sensitive
Z is combinational and by putting it in always an extra flop would berequired leading to extra clock cycle Mealy design of the sequence I/O Declaration is the same as moore 1-bit Full Adder/SUBTRACTOR: Equations for the above circuit:
(W = sub XOR y); 1s compliment of w (S = X XOR W XOR Cin); Computing the sum using Binary Arithmetic (Cout = X * W + X * Cin + W * Cin); Choosing W chooses if its addition orsubtraction 1 bit Adder/Subtractor : Structural Description: 4-bit adder subtractor from 1-BIT MODULE, 4 instantiations vectored signals: Specifying all bits individually is cumbersome. Use vectored signals for acleaner code. input [3:0] x; (Makes x a 4 bit quantity) x[3] MSB, x[2], x[1], x[0] LSB Input [15:0] x; (Represents vector x with16 bit quantity x [15:8]; [Represents an 8 bit vector with the 8 most MSBs], LSB[7:0] x [7:6]; Represents a 2 bit vector consisting of x[7], x[6] 4-bit vectored Adder/subtractor Behavioral 1 bit module to be instantiated: Generalizing the size of a large module
The ripple carry adders we created have a fixed length. If a 32-bit or a 64-bit adder was needed, we would need as many instantiations of FullAddSub. Desirable from designers perspective to define an AddSub module that nnumber of bits can be set to any value. In Verilog such a construct exists, can specify n as : parameter n = 15 andthen write input [n-1:0] x. This case is for 16 bit vector. General description of parameterized I bit adder
Wk = sub XOR Yk, sub is 1 for subtraction and zero for addition Sk = Xk XOR Wk XOR Ck Ck = Xk * Wk + Xk * Ck + Wk * Ck For k = 0, 1, 2---k-1 The for loop: In Verilog the repetitive structure for the of the ripple carry adder/subtractor can bespecified using for procedural statement, (for k=1; k