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////  8051 cores b register                                       ////

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////  This file is part of the 8051 cores project                 ////

////  http://www.opencores.org/cores/8051/                        ////

////                                                              ////

////  Description                                                 ////

////   b register for 8051 core                                   ////

////                                                              ////

////  To Do:                                                      ////

////   Nothing                                                    ////

////                                                              ////

////  Author(s):                                                  ////

////      - Simon Teran, simont@opencores.org                     ////

////                                                              ////

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//// Copyright (C) 2000 Authors and OPENCORES.ORG                 ////

////                                                              ////

//// This source file may be used and distributed without         ////

//// restriction provided that this copyright statement is not    ////

//// removed from the file and that any derivative work contains  ////

//// the original copyright notice and the associated disclaimer. ////

////                                                              ////

//// This source file is free software; you can redistribute it   ////

//// and/or modify it under the terms of the GNU Lesser General   ////

//// Public License as published by the Free Software Foundation; ////

//// either version 2.1 of the License, or (at your option) any   ////

//// later version.                                               ////

////                                                              ////

//// This source is distributed in the hope that it will be       ////

//// useful, but WITHOUT ANY WARRANTY; without even the implied   ////

//// warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR      ////

//// PURPOSE.  See the GNU Lesser General Public License for more ////

//// details.                                                     ////

////                                                              ////

//// You should have received a copy of the GNU Lesser General    ////

//// Public License along with this source; if not, download it   ////

//// from http://www.opencores.org/lgpl.shtml                     ////

////                                                              ////

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//

// CVS Revision History

//

// $Log: not supported by cvs2svn $

//

// synopsys translate_off

`include "oc8051_timescale.v"

// synopsys translate_on

`include "oc8051_defines.v"

module oc8051_b_register (clk, rst, bit_in, bit_out, data_in, wr, wr_bit, wr_addr, rd_addr, data_out);

//

// clk          (in)  clock

// rst          (in)  reset

// bit_in       (in)  bit input - used in case of writing bits to b register (bit adddressable memory space - alu carry) [oc8051_alu.desCy]

// data_in      (in)  data input - used to write to b register [oc8051_alu.des1]

// wr           (in)  write - actine high [oc8051_decoder.wr -r]

// wr_bit       (in)  write bit addresable - actine high [oc8051_decoder.bit_addr -r]

// wr_addr      (in)  write address [oc8051_ram_wr_sel.out]

// data_out     (out) data output [oc8051_ram_sel.b_reg]

//

input clk, rst, wr, wr_bit, bit_in;

input [2:0] rd_addr;

input [7:0] wr_addr, data_in;

output bit_out;

output [7:0] data_out;

reg bit_out;

reg [7:0] data_out;

//

//writing to b

//must check if write high and correct address

always @(posedge clk or posedge rst)

begin

  if (rst)

    data_out <= #1 `OC8051_RST_B;

  else if (wr) begin

    if (!wr_bit) begin

      if (wr_addr==`OC8051_SFR_B)

        data_out <= #1 data_in;

    end else begin

      if (wr_addr[7:3]==`OC8051_SFR_B_B)

        data_out[wr_addr[2:0]] <= #1 bit_in;

    end

  end

end

always @(posedge clk or posedge rst)

begin

  if (rst) bit_out <= #1 1'b0;

  else if ((rd_addr==wr_addr[2:0]) & wr & wr_bit) begin

    bit_out <= #1 bit_in;

  end else if ((wr_addr==`OC8051_SFR_B) & wr & !wr_bit) begin

    bit_out <= #1 data_in[rd_addr];

  end else bit_out <= #1 data_out[rd_addr];

end

endmodule