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[/] [System09/] [trunk/] [rtl/] [System09_Trenz_TE0141/] [ram_controller.vhd] - Rev 155
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-- -- ram_controller.vhd -- library ieee; use ieee.std_logic_1164.all; use ieee.numeric_std.all; use ieee.std_logic_unsigned.all; entity ram_controller is port( reset : in std_logic; clk : in std_logic; cs_ram : in std_logic; rw : in std_logic; din : in std_logic_vector(7 downto 0); dout : out std_logic_vector(7 downto 0); addr : in std_logic_vector(19 downto 0); -- External interface ram_oen : out std_logic; ram_cen : out std_logic; ram_wen : out std_logic; ram_io : inout std_logic_vector(15 downto 0); ram_a : out std_logic_vector(20 downto 1); ram_bhen : out std_logic; ram_blen : out std_logic ); end; architecture external_ram of ram_controller is signal we : std_logic; begin -- -- 1M byte SRAM Control -- Processes to read and write memory based on bus signals -- Uses bhe/ble controlled write -- so that clock stretching can be performed on the CF -- ram_process: process( clk, addr, rw, cs_ram, ram_io, din ) begin ram_wen <= rw; ram_oen <= not rw; ram_cen <= not cs_ram; ram_bhen <= not( (not addr(0)) and clk ); ram_blen <= not( addr(0) and clk ); ram_a(20) <= '0'; ram_a(19 downto 1) <= addr(19 downto 1); if (rw = '0') and (addr(0) = '0') then ram_io(15 downto 8) <= din; else ram_io(15 downto 8) <= "ZZZZZZZZ"; end if; if (rw = '0') and (addr(0) = '1') then ram_io(7 downto 0) <= din; else ram_io(7 downto 0) <= "ZZZZZZZZ"; end if; if addr(0) = '0' then dout <= ram_io(15 downto 8); else dout <= ram_io(7 downto 0); end if; end process; end;
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