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--=============================================================================-- -- -- -- System09 - Synthesizable System On a Chip - VHDL FPGA core top level file. -- -- -- --=============================================================================-- -- -- -- File name : System09_Digilent_3S200.vhd -- -- Entity name : System09 -- -- Purpose : Top level file for 6809 compatible system on a chip -- Designed with Xilinx XC3S200 Spartan 3 FPGA. -- Implemented With Digilent Xilinx Starter FPGA board, -- -- Dependencies : ieee.Std_Logic_1164 -- ieee.std_logic_unsigned -- ieee.std_logic_arith -- ieee.numeric_std -- -- Uses : cpu09 (..\VHDL\cpu09.vhd) CPU core -- dat_ram (..\VHDL\datram.vhd) Dynamic Address Translation -- SYS09BUG_F800 (..\Spartan3\sys093s3_b16.vhd) Monitor ROM -- acia6850 (..\VHDL\acia6850.vhd) ACIA (UART) -- ACIA_Clock (..\VHDL\ACIA_Clock.vhd) ACIA Baud Rate Clock Divider -- keyboard (..\VHDL\keyboard.vhd) PS/2 Keyboard register interface -- ps2_keyboard (..\VHDL\ps2_keyboard.vhd) PS/2 Keyboard interface logic -- keymap_rom (..\Spartan2\keymap_rom.vhd) PS/2 Keyboard key code look up table -- vdu8 (..\VHDL\vdu8.vhd) Video Display Unit -- (..\Spartan3\char_rom2K_b16.vhd) Character Generator ROM (B16_RAM) -- (..\Spartan3\ram2k_b16.vhd) Text & Attribute RAM Buffer -- seven_segment (..\VHDL\SevenSegment.vhd) Seven Segment Display -- -- Author : John E. Kent -- dilbert57@opencores.org -- -- Memory Map : -- -- $0000 - $DFFF System RAM (256K Mapped via DAT) -- $E000 - ACIA (SWTPc) -- $E010 - Reserved for SWTPc FD-01 FD1771 FDC -- $E020 - Keyboard -- $E030 - VDU -- $E040 - Reserved for SWTPc MP-T (was Compact Flash) -- $E050 - Timer -- $E060 - Reserved for Bus Trap (Hardware Breakpoint Logic) -- $E070 - Reserved for Trace Buffer -- $E080 - Reserved for SWTPc MP-ID 6821 PIA (?) -- $E090 - Reserved for SWTPc MP-ID 6840 PTM (?) -- $E0A0 - Switches in / LEDS out -- $E0B0 - 7 Segment display -- $E0C0 - Reserved -- $E0D0 - Reserved -- $E0E0 - Reserved -- $E0F0 - Reserved -- $E100 - $E13F Reserved IDE / Compact Flash Card -- $E140 - $E17F Reserved for Ethernet MAC (XESS) -- $E180 - $E1BF Reserved for Expansion Slot 0 (XESS) -- $E1C0 - $E1FF Reserved for Expansion Slot 1 (XESS) -- $E200 - $EFFF Reserved for Future I/O -- $F000 - $F7FF RAM for Sys09bug monitor extensions -- $F800 - $FFFF Sys09bug ROM (Read only) -- $FFF0 - $FFFF DAT - Dynamic Address Translation (Write Only) -- -- -- Copyright (C) 2003 - 2010 John Kent -- -- This program 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 3 of the License, or -- (at your option) any later version. -- -- This program 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 this program. If not, see <http://www.gnu.org/licenses/>. -- --===========================================================================-- -- -- Revision History: -- --===========================================================================-- -- -- Version 0.1 - 20 March 2003 -- Version 0.2 - 30 March 2003 -- Version 0.3 - 29 April 2003 -- Version 0.4 - 29 June 2003 -- -- Version 0.5 - 19 July 2003 -- prints out "Hello World" -- -- Version 0.6 - 5 September 2003 -- Runs SBUG -- -- Version 1.0- 6 Sep 2003 - John Kent -- Inverted sys_clk -- Initial release to Open Cores -- -- Version 1.1 - 17 Jan 2004 - John Kent -- Updated miniUart. -- -- Version 1.2 - 25 Jan 2004 - John Kent -- removed signals "test_alu" and "test_cc" -- Trap hardware re-instated. -- -- Version 1.3 - 11 Feb 2004 - John Kent -- Designed forked off to produce System09_VDU -- Added VDU component -- VDU runs at 25MHz and divides the clock by 2 for the CPU -- UART Runs at 57.6 Kbps -- -- Version 2.0 - 2 September 2004 - John Kent -- ported to Digilent Xilinx Spartan3 starter board -- removed Compaact Flash and Trap Logic. -- Replaced SBUG with KBug9s -- -- Version 2.1 - 21 November 2006 - John Kent -- Replaced KBug9s with Sys09bug 1.0 -- Inverted bottom nybble of DAT register outputs -- Changed ROM & I/O decoding to be compatible with SWTPc -- Upped the serial baud rate to 115.2 KBd -- added multiple global clock buffers -- (Uart would not operate correctly) -- -- Version 2.2 - 22 December 2006 - John Kent -- Increased CPU clock from 12.5MHz to 25 MHz. -- Removed some of the global clock buffers -- Added LED output register -- Changed address decoding to 4K Blocks -- -- Version 2.3 - 1 June 2007 - John Kent -- Updated VDU & ACIA -- Changed decoding for Sys09Bug -- -- Version 2.4 - 31 January 2008 - John Kent -- ACIA does not appear to work. -- Made RAM OE and WE strobes synchonous to sys_clk -- -- Version 2.5 - 23rd Feburary 2009 - John Kent -- Implemented recommendation to remove vga_clk clock buffer -- -- Version 2.6 - 5th september 2010 - John Kent -- Renamed ACIA_6850 to acia6850 -- Updated generics on VDU8 -- Shortened the "keyboard" label -- Fixed up address label on CPU09 -- Removed Flex RAM -- Map RAM at $F000 - $F7FF -- --===========================================================================-- library ieee; use ieee.std_logic_1164.all; use IEEE.STD_LOGIC_ARITH.ALL; use IEEE.STD_LOGIC_UNSIGNED.ALL; use ieee.numeric_std.all; entity system09 is port( sys_clk : in Std_Logic; -- System Clock input rst_sw : in Std_logic; -- Master Reset input (active high) nmi_sw : in Std_logic; -- Memory Interface signals ram_addr : out Std_Logic_Vector(17 downto 0); ram_wen : out Std_Logic; ram_oen : out Std_Logic; ram1_cen : out Std_Logic; ram1_ubn : out Std_Logic; ram1_lbn : out Std_Logic; ram1_data : inout Std_Logic_Vector(15 downto 0); ram2_cen : out Std_Logic; ram2_ubn : out Std_Logic; ram2_lbn : out Std_Logic; ram2_data : inout Std_Logic_Vector(15 downto 0); -- PS/2 Keyboard ps2c : inout Std_logic; ps2d : inout Std_Logic; -- ACIA Interface rxd : in Std_Logic; txd : out Std_Logic; -- CRTC output signals vs : out Std_Logic; hs : out Std_Logic; blue : out std_logic; green : out std_logic; red : out std_logic; -- LEDS & Switches leds : out std_logic_vector(7 downto 0); switches : in std_logic_vector(7 downto 0); -- seven segment display segments : out std_logic_vector(7 downto 0); digits : out std_logic_vector(3 downto 0) ); end system09; ------------------------------------------------------------------------------- -- Architecture for System09 ------------------------------------------------------------------------------- architecture my_computer of system09 is ----------------------------------------------------------------------------- -- constants ----------------------------------------------------------------------------- constant SYS_CLK_FREQ : integer := 50000000; -- FPGA System Clock constant VGA_CLK_FREQ : integer := 25000000; -- VGA Pixel Clock constant CPU_CLK_FREQ : integer := 25000000; -- CPU Clock constant BAUD_Rate : integer := 57600; -- Baud Rate constant ACIA_CLK_FREQ : integer := BAUD_Rate * 16; type hold_state_type is ( hold_release_state, hold_request_state ); ----------------------------------------------------------------------------- -- Signals ----------------------------------------------------------------------------- -- CPU Interface signals signal cpu_clk : Std_Logic; signal cpu_rst : Std_Logic; signal cpu_rw : std_logic; signal cpu_vma : std_logic; signal cpu_halt : std_logic; signal cpu_hold : std_logic; signal cpu_firq : std_logic; signal cpu_irq : std_logic; signal cpu_nmi : std_logic; signal cpu_addr : std_logic_vector(15 downto 0); signal cpu_data_in : std_logic_vector(7 downto 0); signal cpu_data_out : std_logic_vector(7 downto 0); -- Dynamic Address Translation signal dat_cs : std_logic; signal dat_addr : std_logic_vector(7 downto 0); -- BOOT ROM signal rom_cs : Std_logic; signal rom_data_out : Std_Logic_Vector(7 downto 0); -- ACIA Interface signals signal acia_clk : std_logic; signal acia_cs : Std_Logic; signal acia_data_out : Std_Logic_Vector(7 downto 0); signal acia_irq : Std_Logic; signal acia_rxd : Std_Logic; signal acia_txd : Std_Logic; signal acia_dcd_n : Std_Logic; -- signal acia_rts_n : Std_Logic; signal acia_cts_n : Std_Logic; -- keyboard port signal kbd_data_out : std_logic_vector(7 downto 0); signal kbd_cs : std_logic; signal kbd_irq : std_logic; -- LEDs signal leds_data_out : std_logic_vector(7 downto 0); signal leds_cs : std_logic; -- Video Display Unit signal vdu_cs : std_logic; signal vdu_data_out : std_logic_vector(7 downto 0); signal vga_clk : std_logic; -- 7 Segment Display signal seg_cs : std_logic; signal seg_data_out : std_logic_vector(7 downto 0); -- RAM signal ram_cs : std_logic; -- memory chip select signal ram_data_out : std_logic_vector(7 downto 0); signal ram1_ce : std_logic; signal ram1_ub : std_logic; signal ram1_lb : std_logic; signal ram2_ce : std_logic; signal ram2_ub : std_logic; signal ram2_lb : std_logic; signal ram_we : std_logic; signal ram_oe : std_logic; -- System Clock Prescaler signal clk_count : std_logic; ----------------------------------------------------------------- -- -- CPU09 CPU core -- ----------------------------------------------------------------- component cpu09 port ( clk : in std_logic; rst : in std_logic; vma : out std_logic; addr : out std_logic_vector(15 downto 0); rw : out std_logic; data_in : in std_logic_vector(7 downto 0); data_out : out std_logic_vector(7 downto 0); halt : in std_logic; hold : in std_logic; irq : in std_logic; nmi : in std_logic; firq : in std_logic ); end component; ---------------------------------------- -- -- Dynamic Address Translation Registers -- ---------------------------------------- component dat_ram port ( clk : in std_logic; rst : in std_logic; cs : in std_logic; rw : in std_logic; addr_lo : in std_logic_vector(3 downto 0); addr_hi : in std_logic_vector(3 downto 0); data_in : in std_logic_vector(7 downto 0); data_out : out std_logic_vector(7 downto 0) ); end component; ---------------------------------------- -- -- 4KByte Block RAM Monitor ROM -- ---------------------------------------- component SYS09BUG_F800 Port ( clk : in std_logic; rst : in std_logic; cs : in std_logic; rw : in std_logic; addr : in std_logic_vector (10 downto 0); data_in : in std_logic_vector (7 downto 0); data_out : out std_logic_vector (7 downto 0) ); end component; ----------------------------------------------------------------- -- -- 6850 ACIA -- ----------------------------------------------------------------- component acia6850 port ( clk : in Std_Logic; -- System Clock rst : in Std_Logic; -- Reset input (active high) cs : in Std_Logic; -- ACIA Chip Select rw : in Std_Logic; -- Read / Not Write addr : in Std_Logic; -- Register Select data_in : in Std_Logic_Vector(7 downto 0); -- Data Bus In data_out : out Std_Logic_Vector(7 downto 0); -- Data Bus Out irq : out Std_Logic; -- Interrupt RxC : in Std_Logic; -- Receive Baud Clock TxC : in Std_Logic; -- Transmit Baud Clock RxD : in Std_Logic; -- Receive Data TxD : out Std_Logic; -- Transmit Data DCD_n : in Std_Logic; -- Data Carrier Detect CTS_n : in Std_Logic; -- Clear To Send RTS_n : out Std_Logic -- Request To send ); end component; ----------------------------------------------------------------- -- -- ACIA Clock divider -- ----------------------------------------------------------------- component ACIA_Clock generic ( SYS_CLK_FREQ : integer := SYS_CLK_FREQ; ACIA_CLK_FREQ : integer := ACIA_CLK_FREQ ); port ( clk : in Std_Logic; -- System Clock Input acia_clk : out Std_logic -- ACIA Clock output ); end component; ---------------------------------------- -- -- PS/2 Keyboard -- ---------------------------------------- component keyboard generic( KBD_CLK_FREQ : integer := CPU_CLK_FREQ ); port( clk : in std_logic; rst : in std_logic; cs : in std_logic; addr : in std_logic; rw : in std_logic; data_in : in std_logic_vector(7 downto 0); data_out : out std_logic_vector(7 downto 0); irq : out std_logic; kbd_clk : inout std_logic; kbd_data : inout std_logic ); end component; ---------------------------------------- -- -- Video Display Unit. -- ---------------------------------------- component vdu8 generic( VGA_CLK_FREQ : integer := VGA_CLK_FREQ; -- HZ VGA_HOR_CHARS : integer := 80; -- CHARACTERS 25.6us VGA_HOR_CHAR_PIXELS : integer := 8; -- PIXELS 0.32us VGA_HOR_FRONT_PORCH : integer := 16; -- PIXELS 0.64us VGA_HOR_SYNC : integer := 96; -- PIXELS 3.84us VGA_HOR_BACK_PORCH : integer := 48; -- PIXELS 1.92us VGA_VER_CHARS : integer := 25; -- CHARACTERS 12.8ms VGA_VER_CHAR_LINES : integer := 16; -- LINES 0.512ms VGA_VER_FRONT_PORCH : integer := 10; -- LINES 0.320ms VGA_VER_SYNC : integer := 2; -- LINES 0.064ms VGA_VER_BACK_PORCH : integer := 34 -- LINES 1.088ms ); port( -- control register interface vdu_clk : in std_logic; -- CPU Clock - 12.5MHz vdu_rst : in std_logic; vdu_cs : in std_logic; vdu_rw : in std_logic; vdu_addr : in std_logic_vector(2 downto 0); vdu_data_in : in std_logic_vector(7 downto 0); vdu_data_out : out std_logic_vector(7 downto 0); -- vga port connections vga_clk : in std_logic; -- VGA Pixel Clock - 25 MHz vga_red_o : out std_logic; vga_green_o : out std_logic; vga_blue_o : out std_logic; vga_hsync_o : out std_logic; vga_vsync_o : out std_logic ); end component; ---------------------------------------- -- -- Seven Segment Display driver -- ---------------------------------------- component seven_segment is port ( clk : in std_logic; rst : in std_logic; cs : in std_logic; addr : in std_logic_vector(1 downto 0); rw : in std_logic; data_in : in std_logic_vector(7 downto 0); data_out : out std_logic_vector(7 downto 0); segments : out std_logic_vector(7 downto 0); digits : out std_logic_vector(3 downto 0) ); end component; component BUFG port ( i : in std_logic; o : out std_logic ); end component; begin ----------------------------------------------------------------------------- -- Instantiation of internal components ----------------------------------------------------------------------------- my_cpu : cpu09 port map ( clk => cpu_clk, rst => cpu_rst, vma => cpu_vma, addr => cpu_addr(15 downto 0), rw => cpu_rw, data_in => cpu_data_in, data_out => cpu_data_out, halt => cpu_halt, hold => cpu_hold, irq => cpu_irq, nmi => cpu_nmi, firq => cpu_firq ); my_dat : dat_ram port map ( clk => cpu_clk, rst => cpu_rst, cs => dat_cs, addr_hi => cpu_addr(15 downto 12), addr_lo => cpu_addr(3 downto 0), rw => cpu_rw, data_in => cpu_data_out, data_out => dat_addr(7 downto 0) ); my_rom : SYS09BUG_F800 port map ( clk => cpu_clk, rst => cpu_rst, cs => rom_cs, rw => '1', addr => cpu_addr(10 downto 0), data_in => cpu_data_out, data_out => rom_data_out ); my_acia : acia6850 port map ( clk => cpu_clk, rst => cpu_rst, cs => acia_cs, addr => cpu_addr(0), rw => cpu_rw, data_in => cpu_data_out, data_out => acia_data_out, irq => acia_irq, RxC => acia_clk, TxC => acia_clk, RxD => acia_rxd, TxD => acia_txd, DCD_n => acia_dcd_n, CTS_n => acia_cts_n, RTS_n => open ); ---------------------------------------- -- -- ACIA Clock -- ---------------------------------------- my_ACIA_Clock : ACIA_Clock generic map( SYS_CLK_FREQ => SYS_CLK_FREQ, ACIA_CLK_FREQ => ACIA_CLK_FREQ ) port map( clk => sys_clk, acia_clk => acia_clk ); ---------------------------------------- -- -- PS/2 Keyboard Interface -- ---------------------------------------- my_keyboard : keyboard generic map ( KBD_CLK_FREQ => CPU_CLK_FREQ ) port map( clk => cpu_clk, rst => cpu_rst, cs => kbd_cs, addr => cpu_addr(0), rw => cpu_rw, data_in => cpu_data_out(7 downto 0), data_out => kbd_data_out(7 downto 0), irq => kbd_irq, kbd_clk => ps2c, kbd_data => ps2d ); ---------------------------------------- -- -- Video Display Unit instantiation -- ---------------------------------------- my_vdu : vdu8 generic map( VGA_CLK_FREQ => VGA_CLK_FREQ, -- 25MHZ VGA_HOR_CHARS => 80, -- CHARACTERS 25.6us VGA_HOR_CHAR_PIXELS => 8, -- PIXELS 0.32us VGA_HOR_FRONT_PORCH => 16, -- PIXELS 0.64us VGA_HOR_SYNC => 96, -- PIXELS 3.84us VGA_HOR_BACK_PORCH => 48, -- PIXELS 1.92us VGA_VER_CHARS => 25, -- CHARACTERS 12.8ms VGA_VER_CHAR_LINES => 16, -- LINES 0.512ms VGA_VER_FRONT_PORCH => 10, -- LINES 0.320ms VGA_VER_SYNC => 2, -- LINES 0.064ms VGA_VER_BACK_PORCH => 34 -- LINES 1.088ms ) port map( -- Control Registers vdu_clk => cpu_clk, -- 12.5 MHz System Clock in vdu_rst => cpu_rst, vdu_cs => vdu_cs, vdu_addr => cpu_addr(2 downto 0), vdu_rw => cpu_rw, vdu_data_in => cpu_data_out, vdu_data_out => vdu_data_out, -- vga port connections vga_clk => vga_clk, -- 25 MHz VDU pixel clock vga_red_o => red, vga_green_o => green, vga_blue_o => blue, vga_hsync_o => hs, vga_vsync_o => vs ); ---------------------------------------- -- -- Seven Segment Display instantiation -- ---------------------------------------- my_seg : seven_segment port map ( clk => cpu_clk, rst => cpu_rst, cs => seg_cs, rw => cpu_rw, addr => cpu_addr(1 downto 0), data_in => cpu_data_out, data_out => seg_data_out, segments => segments, digits => digits ); --vga_clk_buffer : BUFG port map( -- i => clk_count, -- o => vga_clk -- ); vga_clk <= cpu_clk; cpu_clk_buffer : BUFG port map( i => clk_count, o => cpu_clk ); -- -- Clock divider -- Assumes 50 MHz system clock -- 25MHz pixel clock -- 25MHz CPU clock -- sys09_clock : process( sys_clk, clk_count ) begin if sys_clk'event and sys_clk='1' then clk_count <= not clk_count; end if; end process; ---------------------------------------------------------------------- -- -- Process to decode memory map -- ---------------------------------------------------------------------- mem_decode: process( cpu_addr, cpu_rw, cpu_vma, dat_cs, dat_addr, rom_data_out, acia_data_out, kbd_data_out, vdu_data_out, seg_data_out, leds_data_out, ram_data_out ) begin cpu_data_in <= (others=>'0'); dat_cs <= '0'; rom_cs <= '0'; acia_cs <= '0'; kbd_cs <= '0'; vdu_cs <= '0'; seg_cs <= '0'; leds_cs <= '0'; ram_cs <= '0'; -- timer_cs <= '0'; -- trap_cs <= '0'; -- pb_cs <= '0'; -- ide_cs <= '0'; -- ether_cs <= '0'; -- slot1_cs <= '0'; -- slot2_cs <= '0'; if cpu_addr( 15 downto 8 ) = "11111111" then cpu_data_in <= rom_data_out; dat_cs <= cpu_vma; -- write DAT rom_cs <= cpu_vma; -- read ROM -- -- Sys09Bug Monitor ROM $F000 - $FFFF -- elsif dat_addr(3 downto 0) = "1111" then -- $XF000 - $XFFFF if cpu_addr(11) = '1' then -- -- Monitor ROM $F800 - $FFFF -- cpu_data_in <= rom_data_out; rom_cs <= cpu_vma; -- read ROM else -- -- SRAM $F000 - $F7FF -- cpu_data_in <= ram_data_out; ram_cs <= cpu_vma; end if; -- -- IO Devices $E000 - $EFFF -- elsif dat_addr(3 downto 0) = "1110" then -- $XE000 - $XEFFF case cpu_addr(11 downto 8) is -- -- SWTPC peripherals from $E000 to $E0FF -- when "0000" => case cpu_addr(7 downto 4) is -- -- ACIA ($E000 - $E00F) -- when "0000" => cpu_data_in <= acia_data_out; acia_cs <= cpu_vma; -- -- Reserved - FD1771 FDC ($E010 - $E01F) (SWTPC) -- -- -- Keyboard port ($E020 - $E02F) -- when "0010" => cpu_data_in <= kbd_data_out; kbd_cs <= cpu_vma; -- -- VDU port ($E030 - $E03F) -- when "0011" => cpu_data_in <= vdu_data_out; vdu_cs <= cpu_vma; -- -- Reserved - SWTPc MP-T ($E040 - $E04F) -- -- -- Reserved - Timer ($E050 - $E05F) (B5-X300) -- -- -- Reserved - Bus Trap Logic ($E060 - $E06F) (B5-X300) -- -- -- Reserved - I/O port ($E070 - $E07F) (B5-X300) -- -- -- Reserved - PTM 6840 ($E080 - $E08F) (SWTPC) -- -- -- Reserved - PIA Timer ($E090 - $E09F) (SWTPC) -- -- -- Read Switched port ($E0A0 - $E0AF) -- Write LEDS -- when "1010" => cpu_data_in <= leds_data_out; leds_cs <= cpu_vma; -- -- 7 segment display port ($E0B0 - $E0BF) -- when "1011" => cpu_data_in <= seg_data_out; seg_cs <= cpu_vma; when others => -- $EXC0 to $EXFF null; end case; -- -- $E100 to $EFFF reserved for future use -- when others => null; end case; -- -- Everything else is RAM -- else cpu_data_in <= ram_data_out; ram_cs <= cpu_vma; end if; end process; -- -- 1M byte SRAM Control -- Processes to read and write memory based on bus signals -- ram_process: process( cpu_rst, sys_clk, cpu_addr, cpu_rw, cpu_vma, cpu_data_out, dat_addr, ram_cs, ram1_ce, ram1_ub, ram1_lb, ram1_data, ram2_ce, ram2_ub, ram2_lb, ram2_data, ram_we, ram_oe ) begin -- -- ram_hold signal helps -- if( cpu_rst = '1' ) then ram_we <= '0'; ram_oe <= '0'; -- -- Clock Hold on rising edge -- elsif( sys_clk'event and sys_clk='1' ) then if (ram_cs = '1') and (ram_we = '0') and (ram_oe = '0') then ram_we <= not cpu_rw; ram_oe <= cpu_rw; else ram_we <= '0'; ram_oe <= '0'; end if; end if; ram_wen <= not ram_we; ram_oen <= not ram_oe; ram1_ce <= ram_cs and (not cpu_addr(1)); ram1_ub <= not cpu_addr(0); ram1_lb <= cpu_addr(0); ram1_cen <= not ram1_ce; ram1_ubn <= not ram1_ub; ram1_lbn <= not ram1_lb; ram2_ce <= ram_cs and cpu_addr(1); ram2_ub <= not cpu_addr(0); ram2_lb <= cpu_addr(0); ram2_cen <= not ram2_ce; ram2_ubn <= not ram2_ub; ram2_lbn <= not ram2_lb; ram_addr(17 downto 10) <= dat_addr(7 downto 0); ram_addr(9 downto 0) <= cpu_addr(11 downto 2); if ram_we = '1' and ram1_ce = '1' and ram1_lb = '1' then ram1_data(7 downto 0) <= cpu_data_out; else ram1_data(7 downto 0) <= "ZZZZZZZZ"; end if; if ram_we = '1' and ram1_ce = '1' and ram1_ub = '1' then ram1_data(15 downto 8) <= cpu_data_out; else ram1_data(15 downto 8) <= "ZZZZZZZZ"; end if; if ram_we = '1' and ram2_ce = '1' and ram2_lb = '1' then ram2_data(7 downto 0) <= cpu_data_out; else ram2_data(7 downto 0) <= "ZZZZZZZZ"; end if; if ram_we = '1' and ram2_ce = '1' and ram2_ub = '1' then ram2_data(15 downto 8) <= cpu_data_out; else ram2_data(15 downto 8) <= "ZZZZZZZZ"; end if; case cpu_addr(1 downto 0) is when "00" => ram_data_out <= ram1_data(15 downto 8); when "01" => ram_data_out <= ram1_data(7 downto 0); when "10" => ram_data_out <= ram2_data(15 downto 8); when others => ram_data_out <= ram2_data(7 downto 0); end case; end process; -- -- LEDS output register -- leds_output : process( cpu_clk, cpu_rst, switches ) begin if cpu_rst = '1' then leds <= "00000000"; elsif cpu_clk'event and cpu_clk='0' then if leds_cs = '1' and cpu_rw = '0' then leds <= cpu_data_out; end if; end if; leds_data_out <= switches; end process; -- -- Interrupts and other bus control signals -- interrupts : process( sys_clk, rst_sw, acia_irq, kbd_irq, nmi_sw ) begin if sys_clk'event and sys_clk = '1' then cpu_rst <= rst_sw; -- CPU reset is active high end if; cpu_firq <= kbd_irq; cpu_nmi <= nmi_sw; cpu_irq <= acia_irq; cpu_halt <= '0'; cpu_hold <= '0'; end process; -- -- ACIA pin assignments -- acia_assignments : process( rxd, acia_txd ) begin acia_dcd_n <= '0'; acia_cts_n <= '0'; acia_rxd <= rxd; txd <= acia_txd; end process; end my_computer; --===================== End of architecture =======================--
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