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-- Copyright (C) 2002 Morgan Kaufmann Publishers, Inc
-- This file is part of VESTs (Vhdl tESTs).
-- VESTs is free software; you can redistribute it and/or modify it
-- under the terms of the GNU General Public License as published by the
-- Free Software Foundation; either version 2 of the License, or (at
-- your option) any later version.
-- VESTs 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 General Public License
-- for more details.
-- You should have received a copy of the GNU General Public License
-- along with VESTs; if not, write to the Free Software Foundation,
-- Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA
entity address_decoder is
port ( addr : in work.cpu_types.address;
status : in work.cpu_types.status_value;
mem_sel, int_sel, io_sel : out bit );
end entity address_decoder;
--------------------------------------------------
architecture functional of address_decoder is
constant mem_low : work.cpu_types.address := X"000000";
constant mem_high : work.cpu_types.address := X"EFFFFF";
constant io_low : work.cpu_types.address := X"F00000";
constant io_high : work.cpu_types.address := X"FFFFFF";
begin
mem_decoder :
mem_sel <= '1' when ( work.cpu_types."="(status, work.cpu_types.fetch)
or work.cpu_types."="(status, work.cpu_types.mem_read)
or work.cpu_types."="(status, work.cpu_types.mem_write) )
and addr >= mem_low
and addr <= mem_high else
'0';
int_decoder :
int_sel <= '1' when work.cpu_types."="(status, work.cpu_types.int_ack) else
'0';
io_decoder :
io_sel <= '1' when ( work.cpu_types."="(status, work.cpu_types.io_read)
or work.cpu_types."="(status, work.cpu_types.io_write) )
and addr >= io_low
and addr <= io_high else
'0';
end architecture functional;
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