pc_io.v

采用Verilog语言实现了8255A的功能

/*
   //*************************************************************************
   // Project Name: 8255A的功能设计和分析
   // Module Name : PC_IO
   // Author:		    张文涛
   // Created:		  2006-10-25
   // Modified:     2006-10-29
   // Revision:		  3.0
   //
   //*************************************************************************
   // 需要注意的地方:            
   //*************************************************************************
*/
module  PC_IO(//input
              reset,
              nRD,
              nWR,
              A,
              Din,
              PC_In,
              Control_Data,
              PortC_Out_Ld,
              
              //output
              PortC_Status,
              PC_Out
              );

  //-----端口声明-----
  input       reset;                                        //复位信号;
  input       nRD;                                          //读信号;
  input       nWR;                                          //写信号;
  input       A;                                            //地址信号;
  input[7:0]  Din;                                          //输入数据;
  input[7:0]  PC_In;                                        //C口输入;
  input[6:0]  Control_Data;                                 //来自Control_Logic的控制信号;
  input[7:0]  PortC_Out_Ld;                                 //C口输出允许信号;
  
  output[7:0] PortC_Status;                                 //C口状态字;
  output[7:0] PC_Out;                                       //C口输出数据;
  
  //-----内部寄存器-----
  reg[7:0]    PortC_Status;
  reg[7:0]    PC_Out;
  reg[7:0]    PC_Out_D;
  reg         IBFA;                                         //A口输入缓冲器满信号;
  reg         IBFB;                                         //B口输入缓冲器满信号;
  reg         nOBFA;                                        //A口输出缓冲器满信号;
  reg         nOBFB;                                        //B口输出缓冲器满信号
  reg         INTEA_In;                                     //A口输入中断允许寄存器;
  reg         INTEA_Out;                                    //A口输出中断允许寄存器;
  reg         INTEB;                                        //B口中断允许寄存器;
  reg         INTRA_In;                                     //A口输入中断寄存器;
  reg         INTRB_In;                                     //B口输入中断寄存器;
  reg         INTRA_Out;                                    //A口输出中断寄存器;
  reg         INTRB_Out;                                    //B口输出中断寄存器;
  
  reg[1:0]    nOBFAstate;                                   //相关状态机寄存器;
  reg[1:0]    IBFAstate;
  reg[1:0]    nOBFBstate;
  reg[1:0]    IBFBstate;
  reg[1:0]    INTRA_Instate;
  reg[1:0]    INTRA_Outstate;
  reg[1:0]    INTRB_Instate;
  reg[1:0]    INTRB_Outstate;
  reg[7:0]    PC_Status_Buf;
   
  //-----内部线型变量-----
  wire[1:0]   A;
  wire        PortC_RS;
  wire        Flag;
  wire[1:0]   ModeA;
  wire        ModeB;
  wire        PortA_IO;
  wire        PortB_IO;
  wire        nSTBA;
  wire        nSTBB;
  wire        nACKA;
  wire        nACKB;
  
  //-----控制字-----
  assign  PortC_RS = Control_Data[6];
  assign  Flag     = Control_Data[5];
  assign  ModeA    = Control_Data[4:3];
  assign  ModeB    = Control_Data[2];
  assign  PortA_IO = Control_Data[1];
  assign  PortB_IO = Control_Data[0];
  assign  nSTBA    = PC_In[4];
  assign  nSTBB    = PC_In[2];
  assign  nACKA    = PC_In[6];
  assign  nACKB    = PC_In[2];
                    	
//////////////////////////////////////////////////////////////////////////
//////////////////////////////PC_Out//////////////////////////////////////
//////////////////////////////////////////////////////////////////////////

  //-----PC_Out-----
  always @ (reset or Flag or PortC_Out_Ld or PC_Out_D)
    if(reset)                                                         //复位清0;
                      PC_Out = 8'b00000000;
    else if(Flag==1'b0)                                               //置位/复位操作;
      case(PortC_Out_Ld)
        8'b11111110:  PC_Out = {PC_Out[7:1],PortC_RS};
        8'b11111101:  PC_Out = {PC_Out[7:2],PortC_RS,PC_Out[0]};
        8'b11111011:  PC_Out = {PC_Out[7:3],PortC_RS,PC_Out[1:0]};
        8'b11110111:  PC_Out = {PC_Out[7:4],PortC_RS,PC_Out[2:0]};
        8'b11101111:  PC_Out = {PC_Out[7:5],PortC_RS,PC_Out[3:0]};
        8'b11011111:  PC_Out = {PC_Out[7:6],PortC_RS,PC_Out[4:0]};
        8'b10111111:  PC_Out = {PC_Out[7],PortC_RS,PC_Out[5:0]};
        8'b01111111:  PC_Out = {PortC_RS,PC_Out[6:0]};
        default:      PC_Out = 8'b11111111;
      endcase
    else
                      PC_Out = PC_Out_D; 
   
   //-----PC_Out_D[7]-----                                           
   always @ (reset or PortC_Out_Ld[7] or nOBFA or Din[7])
     if(PortC_Out_Ld[7]==1'b0)
       PC_Out_D[7] = Din[7];                                     
     else                                                         
       PC_Out_D[7] = nOBFA; 
                     
  //-----PC_Out_D[6]-----                                            
  always @ (reset or PortC_Out_Ld[6] or Din[6])
     if(PortC_Out_Ld[6]==1'b0)
       PC_Out_D[6] = Din[6];                                     
     else                                                         
       PC_Out_D[6] = PC_Out[6];
       
  //-----PC_Out_D[5]-----                                            
  always @ (reset or PortC_Out_Ld[5] or IBFA or Din[5])
     if(PortC_Out_Ld==1'b0)
       PC_Out_D[5] = Din[5];                                     
     else                                                         
       PC_Out_D[5] = IBFA;                                 
         
  //-----PC_Out_D[4]-----                                            
  always @ (reset or PortC_Out_Ld[4] or Din[4])
     if(PortC_Out_Ld[4]==1'b0)
       PC_Out_D[4] = Din[4];                                     
     else                                                         
       PC_Out_D[4] = PC_Out[4];     
  
  //-----PC_Out_D[3]-----                                             
  always @ (reset or PortC_Out_Ld[3] or INTRA_In or INTRA_Out or INTEA_In or INTEA_Out
                  or PortA_IO or Din[3])                     
     if(PortC_Out_Ld[3]==1'b0)
       PC_Out_D[3] = Din[3];                                     
     else if(PortA_IO==1'b0)                                                       
       PC_Out_D[3] = INTRA_In&INTEA_In;
     else
       PC_Out_D[3] = INTRA_Out&INTEA_Out;                                
       
  //-----PC_Out_D[2]-----                                           //nSTBB
  always @ (reset or PortC_Out_Ld[2] or Din[2] or PC_Out[2]) 
     if(PortC_Out_Ld[2]==1'b0)
       PC_Out_D[2] = Din[2];                                     
     else                                                         
       PC_Out_D[2] = PC_Out[2];
 
  //-----PC_Out_D[1]-----
  always @ (reset or PortC_Out_Ld[1] or PortB_IO or IBFB or nOBFB or Din[1])
     if(PortC_Out_Ld[1]==1'b0)
       PC_Out_D[1] = Din[1];                                     
     else if(PortB_IO==1'b0)                                                         
       PC_Out_D[1] = IBFB;
     else
       PC_Out_D[1] = nOBFB;             
       
  //-----PC_Out_D[0]-----                                             //INTRB
  always @ (reset or PortC_Out_Ld[0] or INTRB_In or INTRB_Out or INTEB 
                  or PortB_IO or Din[0])
     if(PortC_Out_Ld[0]==1'b0)
       PC_Out_D[0] = Din[0];                                     
     else if(PortB_IO==1'b0)                                                        
       PC_Out_D[0] = INTRB_In&INTEB;
     else
       PC_Out_D[0] = INTRB_Out&INTEB;  
 
//////////////////////////////////////////////////////////////////////////
//////////////////////////////PortC_Status////////////////////////////////
//////////////////////////////////////////////////////////////////////////
  
  //-----PortC_Status-----
  always @ (reset or PC_Status_Buf)
    if(reset)
            PortC_Status = 8'b00000000;
    else
            PortC_Status = PC_Status_Buf;
            
  //-----PC_Status_Buf[7]-----          
  always @ (PortC_Out_Ld[7] or PC_In[7] or ModeA or PortA_IO or PC_Out[7])
    if(PortC_Out_Ld[7]==1'b0)
      PC_Status_Buf[7] = PC_In[7];
    else if(ModeA==2'b01 && PortA_IO==1'b0)
      PC_Status_Buf[7] = PC_In[7];
    else if((ModeA==2'b01 && PortA_IO==1'b1) || ModeA==2'b10)
      PC_Status_Buf[7] = PC_Out[7];
    else
      PC_Status_Buf[7] = PortC_Status[7];
  
  //-----PC_Status_Buf[6]-----
  always @ (PortC_Out_Ld[6] or PC_In[6] or ModeA or PortA_IO or PC_Out[6] or INTEA_Out)
    if(PortC_Out_Ld[6]==1'b0)
      PC_Status_Buf[6] = PC_In[6];
    else if(ModeA==2'b01 && PortA_IO==1'b0)
      PC_Status_Buf[6] = PC_In[6];
    else if((ModeA==2'b01 && PortA_IO==1'b1) || ModeA==2'b10)
      PC_Status_Buf[6] = INTEA_Out;
    else
      PC_Status_Buf[6] = PortC_Status[6];     
 
  //-----PC_Status_Buf[5]-----
  always @ (PortC_Out_Ld[5] or PC_In[5] or ModeA or PortA_IO or PC_Out[5])
    if(PortC_Out_Ld[5]==1'b0)
      PC_Status_Buf[5] = PC_In[5];
    else if(ModeA==2'b01 && PortA_IO==1'b1)
      PC_Status_Buf[5] = PC_In[5];
    else if((ModeA==2'b01 && PortA_IO==1'b0)||ModeA==2'b10)
      PC_Status_Buf[5] = PC_Out[5];    
    else
      PC_Status_Buf[5] = PortC_Status[5]; 
   
  //-----PC_Status_Buf[4]-----
  always @ (PortC_Out_Ld[4] or PC_In[4] or ModeA or PortA_IO or PC_Out[4])
    if(PortC_Out_Ld[4]==1'b0)
      PC_Status_Buf[4] = PC_In[4];
    else if(ModeA==2'b01 && PortA_IO==1'b1)
      PC_Status_Buf[4] = PC_In[4];
    else if((ModeA==2'b01 && PortA_IO==1'b0)||ModeA==2'b10)
      PC_Status_Buf[4] = PC_Out[4];    
    else
      PC_Status_Buf[4] = PortC_Status[4];

 //-----PC_Status_Buf[3]-----
  always @ (PortC_Out_Ld[3] or PC_In[3] or PC_Out[3])
    if(PortC_Out_Ld[3]==1'b0)
      PC_Status_Buf[3] = PC_In[3];
    else 
      PC_Status_Buf[3] = PC_Out[3];
      
  //-----PC_Status_Buf[2]----- 
  always @ (PortC_Out_Ld[2] or PC_In[2] or PC_Out[2] or ModeB)
    if(PortC_Out_Ld[2]==1'b0)
      PC_Status_Buf[2] = PC_In[2];
    else if(ModeB)
      PC_Status_Buf[2] = INTEB;
    else
      PC_Status_Buf[2] = PC_In[2];        
   
  //-----PC_Status_Buf[1]-----
  always @ (PortC_Out_Ld[1] or PC_In[1] or PC_Out[1] or ModeB)
    if(PortC_Out_Ld[1]==1'b0)
      PC_Status_Buf[1] = PC_In[1];
    else if(ModeB)
      PC_Status_Buf[1] = PC_Out[1];
    else
      PC_Status_Buf[1] = PC_In[1];
 
  //-----PC_Status_Buf[0]-----
  always @ (PortC_Out_Ld[0] or PC_In[0] or PC_Out[0] or ModeB)
    if(PortC_Out_Ld[0]==1'b0)
      PC_Status_Buf[0] = PC_In[0];
    else if(ModeB)
      PC_Status_Buf[0] = PC_Out[0];
    else
      PC_Status_Buf[0] = PC_In[0];