SPI Master Slave Verilog code with testbench

          SPI means Serial Peripheral Interface.

          The Serial Peripheral Interface Bus or SPI bus is a synchronous serial data link de facto standard, named by Motorola, that operates in full duplex mode. Devices communicate in master/slave mode where the master device initiates the data frame. Multiple slave devices are allowed with individual slave select (chip select) lines. Sometimes SPI is called a four-wire serial bus, contrasting with three-, two-, and one-wire serial buses. SPI is often referred to as SSI (Synchronous Serial Interface).

SPI MODE 3:
          CHANGE DATA @ NEGEDGE
          read data @posedge

The SPI Mode 3 waveform is

We have seen the working of SPI and the SPI Master in the previous page. Now let us see about the SPI Slave.

Click here to goto SPI MASTER Page.

SPI SLAVE VERILOG MODULE:
       The slave module is simple.  It is just like a shift register with additional control signal SS_bar. The data is sampled in at positive edge of SCK and shifted out at negative edge of SCK. The data transmission of slave is active only when SS_bar input signal is low, otherwise it is disconnected from the bus & Sdout is tri-stated. Other control signals are similar to that of SPI Master Module.

SPI Slave Block Diagram is

The SPI Slave module verilog code is as follows:
//read from  sdin
always @(posedge sck or negedge rstb)
  begin
    if (rstb==0)
        begin rreg = 8'h00;  rdata = 8'h00; done = 0; nb = 0; end   //
    else if (!ss) begin
            if(mlb==0) 
                begin rreg ={sdin,rreg[7:1]}; end
            else    
                begin rreg ={rreg[6:0],sdin}; end 
            nb=nb+1;
            if(nb!=8) done=0;
            else  begin rdata=rreg; done=1; nb=0; end
        end
  end

//send to  sdout
always @(negedge sck or negedge rstb)
  begin
    if (rstb==0)
        begin treg = 8'hFF; end
    else begin
        if(!ss) begin           
            if(nb==0) treg=tdata;
            else begin
               if(mlb==0)
                    begin treg = {1'b1,treg[7:1]}; end
               else 
                    begin treg = {treg[6:0],1'b1}; end           
            end
        end //!ss
     end //rstb   
  end //always

SIMULATION OUPTUT OF SLAVE:

Downloads & Discussion

Click here to goto SPI MASTER Page.

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