VHDL描述的ad转换和ad转换器有什么区别呢？ 有这个还要ad转换器干嘛

有什么区别? 下面是见过的一个VHDL描述的ad转换
Package defining types used by the system memory
PACKAGE rampac IS
SUBTYPE addr10 IS NATURAL RANGE 0 TO 1023;
SUBTYPE data16 IS INTEGER RANGE -32768 TO +32767;
TYPE ram_array IS ARRAY(addr10'LOW TO addr10'HIGH) OF data16;
CONSTANT z_val : data16 := -1;
END rampac;
Package defining a basic analogue type
PACKAGE adcpac IS
SUBTYPE analogue IS REAL RANGE -5.0 TO +5.0;
END adcpac;
16-bit Analogue to Digital Converter
USE WORK.rampac.ALL;
USE WORK.adcpac.ALL;
ENTITY adc16 IS
GENERIC(tconv : TIME := 10 us); --conversion time
PORT(vin : IN analogue; digout : OUT data16; --input and output
sc : IN BIT; busy : OUT BIT); --control
END adc16;
ARCHITECTURE behaviour OF adc16 IS
BEGIN
PROCESS
VARIABLE digtemp : data16;
CONSTANT vlsb : analogue := (analogue'HIGH -
analogue'LOW)/REAL(2*ABS(data16'LOW));
BEGIN
digtemp := data16'LOW;
busy <= '0';
WAIT UNTIL (sc'EVENT AND sc = '0');
busy <= '1';
FOR i IN 0 TO (2*data16'HIGH) LOOP
IF vin >= (analogue'LOW + (REAL(i) + 0.5)*vlsb)
THEN digtemp := digtemp + 1;
ELSE EXIT;
END IF;
END LOOP;
WAIT FOR tconv;
digout <= digtemp;
busy <= '0';
END PROCESS;
END behaviour;

VHDL描述的ad转换和ad转换器有什么区别呢? 有这个还要ad转换器干嘛
这个只是个模型
不是硬件