VHDL implementation of the 6845
From CPCWiki - THE Amstrad CPC encyclopedia!
This code can be used to implement an CRTC6845 in a CPLD or a FPGA. It consists of three files (config.vhd, crtc6845.vhd, cursor.vhd). You can also directly download the source files.
config.vhd
--===========================================================================--
-- --
-- S Y N T H E S I Z A B L E CRTC6845 C O R E --
-- --
-- www.opencores.org - January 2000 --
-- This IP core adheres to the GNU public license. --
-- --
-- VHDL model of MC6845 compatible CRTC --
-- --
-- This model doesn't implement interlace mode. Everything else is --
-- (probably) according to original MC6845 data sheet (except VTOTADJ). --
-- --
-- Implementation in Xilinx Virtex XCV50-6 runs at 50 MHz (character clock).--
-- With external pixel generator this CRTC could handle 450MHz pixel rate --
-- (see MC6845 datasheet for typical application). --
-- --
-- Author: Damjan Lampret, lampret@opencores.org --
-- --
-- TO DO: --
-- --
-- - fix REG_INIT and remove non standard signals at topl level entity. --
-- Allow fixed registers values (now set with REG_INIT). Anyway cleanup --
-- required. --
-- --
-- - split design in four units (horizontal sync, vertical sync, bus --
-- interface and the rest) --
-- --
-- - synthesis with Synplify pending (there are some problems with --
-- UNSIGNED and BIT_LOGIC_VECTOR types in some units !) --
-- --
-- - testbench --
-- --
-- - interlace mode support, extend VSYNC for V.Total Adjust value (R5) --
-- --
-- - verification in a real application --
-- --
--===========================================================================--
library IEEE;
use IEEE.std_logic_1164.all;
use IEEE.std_logic_arith.all;
use IEEE.math_real.all;
package CONFIG is
-- Don't change these unless you know what you are doing.
constant MA_WIDTH : INTEGER := 14;
constant RA_WIDTH : INTEGER := 5;
constant DB_WIDTH : INTEGER := 8;
constant AR_WIDTH : INTEGER := 5;
constant INDEX_HT : STD_LOGIC_VECTOR (4 downto 0) := '0' & x"0";
constant INDEX_HD : STD_LOGIC_VECTOR (4 downto 0) := '0' & x"1";
constant INDEX_HSP : STD_LOGIC_VECTOR (4 downto 0) := '0' & x"2";
constant INDEX_HSW : STD_LOGIC_VECTOR (4 downto 0) := '0' & x"3";
constant INDEX_VT : STD_LOGIC_VECTOR (4 downto 0) := '0' & x"4";
constant INDEX_ADJ : STD_LOGIC_VECTOR (4 downto 0) := '0' & x"5";
constant INDEX_VD : STD_LOGIC_VECTOR (4 downto 0) := '0' & x"6";
constant INDEX_VSP : STD_LOGIC_VECTOR (4 downto 0) := '0' & x"7";
constant INDEX_IM : STD_LOGIC_VECTOR (4 downto 0) := '0' & x"8";
constant INDEX_SL : STD_LOGIC_VECTOR (4 downto 0) := '0' & x"9";
constant INDEX_CURST : STD_LOGIC_VECTOR (4 downto 0) := '0' & x"a";
constant INDEX_CUREND : STD_LOGIC_VECTOR (4 downto 0) := '0' & x"b";
constant INDEX_SA_H : STD_LOGIC_VECTOR (4 downto 0) := '0' & x"c";
constant INDEX_SA_L : STD_LOGIC_VECTOR (4 downto 0) := '0' & x"d";
constant INDEX_CUR_H : STD_LOGIC_VECTOR (4 downto 0) := '0' & x"e";
constant INDEX_CUR_L : STD_LOGIC_VECTOR (4 downto 0) := '0' & x"f";
constant INDEX_LP_H : STD_LOGIC_VECTOR (4 downto 0) := '1' & x"0";
constant INDEX_LP_L : STD_LOGIC_VECTOR (4 downto 0) := '1' & x"1";
-- Convert UNSIGNED type to STD_LOGIC_VECTOR type
function MAKE_BINARY(A : UNSIGNED) return STD_LOGIC_VECTOR;
-- Convert STD_LOGIC_VECTOR type to UNSIGNED type
function MAKE_UNSIGNED(A : STD_LOGIC_VECTOR) return UNSIGNED;
end CONFIG;
package body CONFIG is
-- synopsys synthesis_off
type tbl_type is array (STD_ULOGIC) of STD_ULOGIC;
constant tbl_BINARY : tbl_type :=
('X', 'X', '0', '1', 'X', 'X', '0', '1', 'X');
-- synopsys synthesis_on
function MAKE_BINARY(A : UNSIGNED) return STD_LOGIC_VECTOR is
-- synopsys built_in SYN_FEED_THRU
variable one_bit : STD_ULOGIC;
variable result : STD_LOGIC_VECTOR (A'range);
begin
-- synopsys synthesis_off
for i in A'range loop
result(i) := tbl_BINARY(A(i));
end loop;
return result;
-- synopsys synthesis_on
end;
function MAKE_UNSIGNED(A : STD_LOGIC_VECTOR) return UNSIGNED is
-- synopsys built_in SYN_FEED_THRU
variable one_bit : STD_ULOGIC;
variable result : UNSIGNED (A'range);
begin
-- synopsys synthesis_off
for i in A'range loop
result(i) := tbl_BINARY(A(i));
end loop;
return result;
-- synopsys synthesis_on
end;
end CONFIG;
crtc6845.vhd
--===========================================================================--
-- --
-- S Y N T H E S I Z A B L E CRTC6845 C O R E --
-- --
-- www.opencores.org - January 2000 --
-- This IP core adheres to the GNU public license. --
-- --
-- VHDL model of MC6845 compatible CRTC --
-- --
-- This model doesn't implement interlace mode. Everything else is --
-- (probably) according to original MC6845 data sheet (except VTOTADJ). --
-- --
-- Implementation in Xilinx Virtex XCV50-6 runs at 50 MHz (character clock).--
-- With external pixel generator this CRTC could handle 450MHz pixel rate --
-- (see MC6845 datasheet for typical application). --
-- --
-- Author: Damjan Lampret, lampret@opencores.org --
-- --
-- TO DO: --
-- --
-- - fix REG_INIT and remove non standard signals at topl level entity. --
-- Allow fixed registers values (now set with REG_INIT). Anyway cleanup --
-- required. --
-- --
-- - split design in four units (horizontal sync, vertical sync, bus --
-- interface and the rest) --
-- --
-- - synthesis with Synplify pending (there are some problems with --
-- UNSIGNED and BIT_LOGIC_VECTOR types in some units !) --
-- --
-- - testbench --
-- --
-- - interlace mode support, extend VSYNC for V.Total Adjust value (R5) --
-- --
-- - verification in a real application --
-- --
--===========================================================================--
library IEEE;
use IEEE.std_logic_1164.all;
use IEEE.std_logic_arith.all;
use work.config.all;
entity crtc6845 is
port (
MA : out STD_LOGIC_VECTOR (MA_WIDTH-1 downto 0);
RA : out STD_LOGIC_VECTOR (RA_WIDTH-1 downto 0);
HSYNC : out STD_LOGIC;
VSYNC : out STD_LOGIC;
DE : out STD_LOGIC;
CURSOR : out STD_LOGIC;
LPSTBn : in STD_LOGIC;
E : in STD_LOGIC;
RS : in STD_LOGIC;
CSn : in STD_LOGIC;
RW : in STD_LOGIC;
D : inout STD_LOGIC_VECTOR (DB_WIDTH-1 downto 0);
RESETn : in STD_LOGIC;
CLK : in STD_LOGIC;
-- not standard
REG_INIT: in STD_LOGIC;
--
Hend: inout STD_LOGIC;
HS: inout STD_LOGIC;
CHROW_CLK: inout STD_LOGIC;
Vend: inout STD_LOGIC;
SLadj: inout STD_LOGIC;
H: inout STD_LOGIC;
V: inout STD_LOGIC;
CURSOR_ACTIVE: inout STD_LOGIC;
VERT_RST: inout STD_LOGIC
);
end crtc6845;
architecture crtc6845_behav of crtc6845 is
-- components
component cursor_ctrl
port (
RESETn : in STD_LOGIC;
CLK : in STD_LOGIC;
RA : in STD_LOGIC_VECTOR (RA_WIDTH-1 downto 0);
CURSOR : out STD_LOGIC;
ACTIVE : in STD_LOGIC;
CURST : in STD_LOGIC_VECTOR (6 downto 0);
CUREND : in STD_LOGIC_VECTOR (4 downto 0)
);
end component;
-- 6845 registers R0-R17
signal REG_HT : STD_LOGIC_VECTOR (7 downto 0);
signal REG_HD : STD_LOGIC_VECTOR (7 downto 0);
signal REG_HSP : STD_LOGIC_VECTOR (7 downto 0);
signal REG_HSW : STD_LOGIC_VECTOR (3 downto 0);
signal REG_VT : STD_LOGIC_VECTOR (6 downto 0);
signal REG_ADJ : STD_LOGIC_VECTOR (4 downto 0);
signal REG_VD : STD_LOGIC_VECTOR (6 downto 0);
signal REG_VSP : STD_LOGIC_VECTOR (6 downto 0);
signal REG_IM : STD_LOGIC_VECTOR (1 downto 0);
signal REG_SL : STD_LOGIC_VECTOR (4 downto 0);
signal REG_CURST : STD_LOGIC_VECTOR (6 downto 0);
signal REG_CUREND : STD_LOGIC_VECTOR (4 downto 0);
signal REG_SA_H : STD_LOGIC_VECTOR (5 downto 0);
signal REG_SA_L : STD_LOGIC_VECTOR (7 downto 0);
signal REG_CUR_H : STD_LOGIC_VECTOR (5 downto 0);
signal REG_CUR_L : STD_LOGIC_VECTOR (7 downto 0);
signal REG_LP_H : STD_LOGIC_VECTOR (5 downto 0);
signal REG_LP_L : STD_LOGIC_VECTOR (7 downto 0);
-- Counters
signal CTR_HORIZ : UNSIGNED (7 downto 0);
signal CTR_HSW : UNSIGNED (3 downto 0);
signal CTR_SL : UNSIGNED (4 downto 0);
signal CTR_VERT : UNSIGNED (6 downto 0);
signal CTR_VSW : UNSIGNED (4 downto 0);
signal CTR_LAG : UNSIGNED (13 downto 0);
-- I/O address register
signal REGIO_AR : STD_LOGIC_VECTOR (AR_WIDTH-1 downto 0);
-- Interconnect signals (as in MC6845 datasheet)
--pragma translate_off
signal Hend: STD_LOGIC;
signal HS: STD_LOGIC;
signal CHROW_CLK: STD_LOGIC;
signal Vend: STD_LOGIC;
signal SLadj: STD_LOGIC;
signal H: STD_LOGIC;
signal V: STD_LOGIC;
signal CURSOR_ACTIVE: STD_LOGIC;
signal VERT_RST: STD_LOGIC;
--pragma translate_on
-- Shared Variables
signal Hdisp: STD_LOGIC;
signal Vdisp: STD_LOGIC;
shared variable ROWaddr: UNSIGNED (13 downto 0);
begin
ext_read:
process(E)
begin
if rising_edge(E) then
if CSn = '0' and RW = '1' and RS = '1' then
case REGIO_AR is
when INDEX_CUR_H =>
D(5 downto 0) <= REG_CUR_H;
D(7 downto 6) <= "00";
when INDEX_CUR_L =>
D <= REG_CUR_L;
when INDEX_LP_H =>
D(5 downto 0) <= REG_LP_H;
D(7 downto 6) <= "00";
when INDEX_LP_L =>
D <= REG_LP_L;
when others =>
D <= (others => '0');
end case;
else
D <= (others => 'Z');
end if;
end if;
end process;
ext_write:
process(E,REG_INIT)
begin
if falling_edge(E) then
if REG_INIT = '1' then
REGIO_AR <= b"0" & x"0";
REG_HT <= x"65";
REG_HD <= x"50";
REG_HSP <= x"56";
REG_HSW <= x"9";
REG_SL <= '0' & x"b";
REG_VT <= b"001" & x"8"; --18
REG_ADJ <= b"0" & x"a";
REG_VD <= b"001" & x"8"; --18
REG_VSP <= b"001" & x"8";--18
REG_CURST <= b"000" & x"0";
REG_CUREND <= b"0" & x"B";
REG_SA_H <= b"00" & x"0";
REG_SA_L <= x"80";
REG_CUR_H <= b"00" & x"0";
REG_CUR_L <= x"80";
end if;
end if;
--pragma translate_off
if CSn = '0' and RW = '0' then
if RS = '0' then
REGIO_AR <= D (AR_WIDTH-1 downto 0);
else
case REGIO_AR is
when INDEX_HT =>
REG_HT <= D;
when INDEX_HD =>
REG_HD <= D;
when INDEX_HSP =>
REG_HSP <= D;
when INDEX_HSW =>
REG_HSW <= D(3 downto 0);
when INDEX_SL =>
REG_SL <= D(4 downto 0);
when INDEX_VT =>
REG_VT <= D(6 downto 0);
when INDEX_ADJ =>
REG_ADJ <= D(4 downto 0);
when INDEX_VD =>
REG_VD <= D(6 downto 0);
when INDEX_VSP =>
REG_VSP <= D(6 downto 0);
when INDEX_CURST =>
REG_CURST <= D(6 downto 0);
when INDEX_CUREND =>
REG_CUREND <= D(4 downto 0);
when INDEX_SA_H =>
REG_SA_H <= D(5 downto 0);
when INDEX_SA_L =>
REG_SA_L <= D;
when INDEX_CUR_H =>
REG_CUR_H <= D(5 downto 0);
when INDEX_CUR_L =>
REG_CUR_L <= D;
when others =>
null;
end case;
end if;
end if;
end if;
--pragma translate_on
end process;
--------------------------------------------
-- Horizontal Sync --
--------------------------------------------
H_p:
process(CLK, RESETn)
begin
if RESETn = '0' then
CTR_HORIZ <= (others => '0');
elsif rising_edge(CLK) then
if MAKE_BINARY(CTR_HORIZ) = REG_HT then
H <= '1';
CTR_HORIZ <= (others => '0');
else
H <= '0';
CTR_HORIZ <= CTR_HORIZ + 1;
end if;
end if;
end process;
Hend_p:
process(CTR_HORIZ, REG_HD)
begin
if MAKE_BINARY(CTR_HORIZ) = REG_HD then
Hend <= '1';
else
Hend <= '0';
end if;
end process;
CTR_HSW_p:
process(CLK, RESETn)
begin
if RESETn = '0' then
CTR_HSW <= (others => '0');
elsif rising_edge(CLK) then
if HS = '1' then
CTR_HSW <= CTR_HSW + 1;
else
CTR_HSW <= (others => '0');
end if;
end if;
end process;
HS_p:
process(CTR_HORIZ, CTR_HSW, REG_HSP, REG_HSW, HS)
begin
if MAKE_BINARY(CTR_HORIZ) = REG_HSP then
HS <= '1';
elsif MAKE_BINARY(CTR_HSW) = REG_HSW then
HS <= '0';
else
HS <= HS;
end if;
HSYNC <= HS;
end process;
--------------------------------------------
-- Display Enable --
--------------------------------------------
DE_p:
process(H, Hend, V, Vend, Hdisp, Vdisp)
begin
if H = '1' and Hend = '0' then
Hdisp <= '1';
elsif H = '0' and Hend = '1' then
Hdisp <= '0';
else
Hdisp <= Hdisp;
end if;
if V = '1' and Vend = '0' then
Vdisp <= '1';
elsif V = '0' and Vend = '1' then
Vdisp <= '0';
else
Vdisp <= Vdisp;
end if;
end process;
DE <= Hdisp and Vdisp;
--------------------------------------------
-- Scan Line Counter --
--------------------------------------------
CTR_SL_p:
process(H, RESETn)
begin
if RESETn = '0' then
CTR_SL <= (others => '0');
elsif rising_edge(H) then
if MAKE_BINARY(CTR_SL) = REG_SL then
CHROW_CLK <= '1';
CTR_SL <= (others => '0');
else
CHROW_CLK <= '0';
CTR_SL <= CTR_SL + 1;
end if;
end if;
end process;
RA <= MAKE_BINARY(CTR_SL);
SLadj_p:
process(CTR_SL, REG_ADJ)
begin
if MAKE_BINARY(CTR_SL) = REG_ADJ then
SLadj <= '1';
else
SLadj <= '0';
end if;
end process;
--------------------------------------------
-- Vertical Sync (Character Row CTR) --
--------------------------------------------
V_p:
process(CHROW_CLK, RESETn)
begin
if RESETn = '0' then
CTR_VERT <= (others => '0');
elsif rising_edge(CHROW_CLK) then
if MAKE_BINARY(CTR_VERT) = REG_VT then
V <= '1';
-- if SLadj = '1' then
VERT_RST <= '1';
CTR_VERT <= (others => '0');
-- end if;
else
VERT_RST <= '0';
V <= '0';
CTR_VERT <= CTR_VERT + 1;
end if;
end if;
end process;
Vend_p:
process(CTR_VERT, REG_VD)
begin
if MAKE_BINARY(CTR_VERT) = REG_VD then
Vend <= '1';
else
Vend <= '0';
end if;
end process;
CTR_VSW_p:
process(H, RESETn, CTR_VERT, REG_VSP, CTR_VSW)
begin
if RESETn = '0' then
CTR_VSW <= (others => '0');
elsif rising_edge(H) then
if MAKE_BINARY(CTR_VERT) = REG_VSP then
CTR_VSW <= (others => '0');
end if;
if CTR_VSW /= 16 then
CTR_VSW <= CTR_VSW + 1;
VSYNC <= '1';
else
VSYNC <= '0';
end if;
end if;
end process;
--------------------------------------------
-- Linear Address Generator --
--------------------------------------------
ROWaddr_p:
process(RESETn, CHROW_CLK, VERT_RST, REG_SA_H, REG_SA_L)
begin
if RESETn = '0' then
ROWaddr := MAKE_UNSIGNED(REG_SA_H & REG_SA_L);
elsif rising_edge(CHROW_CLK) then
ROWaddr := ROWaddr + MAKE_UNSIGNED(REG_HD);
if VERT_RST = '1' then
ROWaddr := MAKE_UNSIGNED(REG_SA_H & REG_SA_L);
end if;
end if;
end process;
LAG_p:
process(CLK, RESETn, H, REG_SA_H, REG_SA_L)
begin
if RESETn = '0' then
CTR_LAG <= MAKE_UNSIGNED(REG_SA_H & REG_SA_L);
elsif rising_edge(CLK) then
if H = '1' then
CTR_LAG <= ROWaddr;
end if;
CTR_LAG <= CTR_LAG + 1;
end if;
end process;
MA <= MAKE_BINARY(CTR_LAG);
--------------------------------------------
-- Light Pen Capture --
--------------------------------------------
LP_p:
process(CLK, LPSTBn)
begin
if rising_edge(CLK) then
if LPSTBn = '0' then
REG_LP_H <= MAKE_BINARY(CTR_LAG(13 downto 8));
REG_LP_L <= MAKE_BINARY(CTR_LAG(7 downto 0));
end if;
end if;
end process;
--------------------------------------------
-- Cursor Control Unit Instantiation --
--------------------------------------------
CURSOR_p:
process(CTR_LAG, REG_CUR_H, REG_CUR_L)
begin
if CTR_LAG = MAKE_UNSIGNED(REG_CUR_H & REG_CUR_L) then
CURSOR_ACTIVE <= '1';
else
CURSOR_ACTIVE <= '0';
end if;
end process;
cursor_ctrl_inst: cursor_ctrl
port map (
RESETn => RESETn,
CLK => V,
RA => MAKE_BINARY(CTR_SL),
CURSOR => CURSOR,
ACTIVE => CURSOR_ACTIVE,
CURST => REG_CURST,
CUREND => REG_CUREND
);
end crtc6845_behav;
cursor.vhd
--===========================================================================--
-- --
-- S Y N T H E S I Z A B L E CRTC6845 C O R E --
-- --
-- www.opencores.org - January 2000 --
-- This IP core adheres to the GNU public license. --
-- --
-- VHDL model of MC6845 compatible CRTC --
-- --
-- This model doesn't implement interlace mode. Everything else is --
-- (probably) according to original MC6845 data sheet (except VTOTADJ). --
-- --
-- Implementation in Xilinx Virtex XCV50-6 runs at 50 MHz (character clock).--
-- With external pixel generator this CRTC could handle 450MHz pixel rate --
-- (see MC6845 datasheet for typical application). --
-- --
-- Author: Damjan Lampret, lampret@opencores.org --
-- --
-- TO DO: --
-- --
-- - fix REG_INIT and remove non standard signals at topl level entity. --
-- Allow fixed registers values (now set with REG_INIT). Anyway cleanup --
-- required. --
-- --
-- - split design in four units (horizontal sync, vertical sync, bus --
-- interface and the rest) --
-- --
-- - synthesis with Synplify pending (there are some problems with --
-- UNSIGNED and BIT_LOGIC_VECTOR types in some units !) --
-- --
-- - testbench --
-- --
-- - interlace mode support, extend VSYNC for V.Total Adjust value (R5) --
-- --
-- - verification in a real application --
-- --
--===========================================================================--
library IEEE;
use IEEE.std_logic_1164.all;
use IEEE.std_logic_arith.all;
use work.config.all;
entity cursor_ctrl is
port (
RESETn : in STD_LOGIC;
CLK : in STD_LOGIC;
RA : in STD_LOGIC_VECTOR (RA_WIDTH-1 downto 0);
CURSOR : out STD_LOGIC;
ACTIVE : in STD_LOGIC;
CURST : in STD_LOGIC_VECTOR (6 downto 0);
CUREND : in STD_LOGIC_VECTOR (4 downto 0)
);
end cursor_ctrl;
architecture cursor_ctrl_behav of cursor_ctrl is
signal CTR_BLINK : UNSIGNED (4 downto 0);
begin
blink_ctr_p:
process (CLK, RESETn)
begin
if RESETn = '0' then
CTR_BLINK <= (others => '0');
elsif rising_edge(CLK) then
CTR_BLINK <= CTR_BLINK + 1;
end if;
end process;
cursor_p:
process (ACTIVE, CURST, CUREND, RA, CTR_BLINK)
begin
if RA >= CURST(4 downto 0) and RA <= CUREND and ACTIVE = '1' then
case CURST(6 downto 5) is
when "00" =>
CURSOR <= '1';
when "10" =>
CURSOR <= CTR_BLINK(3);
when "11" =>
CURSOR <= CTR_BLINK(4);
when others =>
CURSOR <= '0';
end case;
else
CURSOR <= '0';
end if;
end process;
end cursor_ctrl_behav;
