/*****************************************//**        8bit RISC MCU desing         **//**           stack module              **//**            BY yuzhijie              **//**            2006.10.26               **//*****************************************/`timescale 1ns/100psmodule stack(clk4,pc_addr,stack_call,stack_retlw,stack1);    input clk4,stack_call,stack_retlw;    input [10:0]pc_addr;     output [10:0]stack1;    reg[10:0]stack1;    reg[10:0]stack[1:0];      //stack[0]top of stackalways@(posedge stack_call or posedge stack_retlw)   begin       if(stack_call==1)        begin           stack[1]<=stack[0];           stack[0]<=pc_addr+1;   //input stack CALL       end       else if(stack_retlw==1)       begin          stack1<=stack[0];          stack[0]<=stack[1];   //output stack RETLW       end    endendmodule