状态机描述.pptVIP

3-* Example: 一段式状态机 描述方法 stop: begin if ( A ) begin state = clear; K2 = 1; end else state = stop; end clear: begin if ( !A) begin state = idle ; {K2,K1} = 2’b01; end else state = clear ; end endcase endmodule module Mealy_state_machine (clock, reset, A, K2, K1 ); input clock, reset, A; output K2, K1; reg K2, K1; reg [1,0] state; parameter idle =2’b00, start =2’b01; stop =2’b10, clear =2’11; always @(posedge clock or negedge reset) if (!reset) begin state = idle; {K2,K1} = 2’b00; end else case (state) idle: begin if ( A) begin state = start ; K1 = 0; end else state = idle ; end 　　　start: begin if ( !A) state = stop ; else state = start ; end 3.5 状态机描述方法 module state_machine (clock, reset, rdy, r_w, oe, we); input clock, reset; input rdy, r_w; output oe,we; reg oe,we; reg [3,0] present_state, next_state; parameter idle =4’b0001, decision=4’b0010; read=4’b0100, write=4’1000; // sequential state transition always @ (posedge clock or negedge reset ) if ( !reset ) present_state = idle ; else present_state = next_state ; //combinational block always @(reset or present_state or rdy or r_w) begin case (present_state) idle: begin {oe,we} = 2’b00; if ( rdy) next_state = decision ; else next_state = idle ;