数字设计基础双语教学版课件作者英BarryWilknson双语课件（第5章节）.pptVIP

尚辅网 / 5. Sequential circuit design 5.1 Synchronous sequential circuit model 5.2 Designing synchronous sequential circuits 5.1 Synchronous sequential circuit model 1. Mealy model The outputs Z are combinational functions of both the present state variables y and the inputs X. 5.1 Synchronous sequential circuit model ? X0…Xn-1 : a set of n inputs, X; ? Z0…Zm-1 : a set of m outputs, Z; ? y0…yk-1 : a set of k internal signals, y, which define the present state of the circuit, i.e. present state variables. ? Y0…Yk-1 : a set of k internal signals, Y, which are generated to produce the next state of the circuit, i.e. next state variables. Y and Z are both combinational functions of the circuit inputs X and the present state y. 5.1 Synchronous sequential circuit model 2. Moore model The outputs Z are combinational functions of only the present state variables y. 5.2 Designing synchronous sequential circuit 1. Design procedure ? Derive the state diagram. ? Draw the state table. ? Assign state variable patterns to states. ? Draw the assigned state table. ? Derive the flip-flop input functions. ? Derive the output function of a Karnaugh map. ? Draw the logic circuit. 5.2 Designing synchronous sequential circuit 2. Design examples Exp1: Suppose a synchronous counter is required which follows one of two repeating sequences depending upon a control input C. When C=0, the sequence is 00, 01, 11. When C=1, the sequence is 00, 11, 01. （1）Derive the state diagram Only three states are in the sequence. The fourth state might appear upon switch-on, so we map it to lead to state 1. State diagram 5.2 Designing synchronous sequential circuit （2）Draw the state transition table State table The state transition table can be constructed from the state diagram. （3）State assignment Values needs to be chosen for the present state variables for each state. For convenience, we assign: y2y1= 00 for state 1; y2y1=