Here are the highlights from the frame buffer display logic in dot88.v

dott88_snippet.v

  always @ (posedge clk)
    begin
      
      // initialise 
      if (!resetn) 
          begin
              pcounter <= 0;
              d88_counter <= 0;
              xp <= 0;
              yp <= 0;
          end

      d88_counter <= d88_counter + 1;

      if (!d88_counter)
        begin
          pcounter <= pcounter + 1;
      
          // calculate position
          xp <= pcounter/8;
          yp <= pcounter - 8*(pcounter/8);  

          // update row/col
          c <= fb[pcounter-1] ? (8'd1 << (7 - xp)) : 8'd0;
          r <= ~(8'd1 << (7 - yp));
        end
        
    end

  assign {row, col} = {r, c};