rom_based_waveform.vhd

含有各类寄存器

--ROM-based waveform generator
PACKAGE rompac IS
CONSTANT rom_width : POSITIVE := 3;
CONSTANT addr_high : POSITIVE := 12;
SUBTYPE rom_word IS BIT_VECTOR(0 TO rom_width);
TYPE rom_table IS ARRAY(0 TO addr_high) OF rom_word;
CONSTANT rom : rom_table :=
("1100",
"1100",
"0100",
"0000",
"0110",
"0101",
"0111",
"1100",
"0100",
"0000",
"0110",
"0101",
"0111");
END rompac;
--WAVEFORM GENERATOR USING A ROM LOOK-UP TABLE 15-6-92
--THE ROM IS A CONSTANT DECLARED WITHIN THE PACKAGE rompac.
--
USE work.rompac.ALL;
ENTITY romwaves IS
PORT(clock : IN BIT; reset : IN BOOLEAN;
waves : OUT rom_word);
END romwaves;
ARCHITECTURE behaviour OF romwaves IS
SIGNAL step : NATURAL;
BEGIN
--address counter for rom look-up table
step_counter:PROCESS
BEGIN
WAIT UNTIL clock'EVENT AND clock = '1';
IF reset THEN --check for reset condition
step <= 0;
ELSIF step = addr_high THEN --check for last wave value
step <= addr_high;
ELSE
step <= step + 1; --get next wave value
END IF;
END PROCESS;
--output value from rom look-up table
waves <= rom(step);
END behaviour;