EDA中VHDL基本逻辑电路设计.docx

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1、第三章基本逻辑电路设计3.1组合逻辑电路设计一、简单门电路设计例：3输入“与非”门电路LIBRARYIEEE;USEIEEE.STD_LOGIC_1164.ALL;ENTITYnand3ISPORT（a，b，c：INSTD_LOGIC;y：OUTSTD_LOGIC）;ENDnand3;ARCHITECTUREnand3_1OFnand3ISBEGINy＜＝NOT（aANDbANDc）;ENDnand3_1;LIBRARYIEEE;USEIEEE.STD_LOGIC_1164.ALL;ENTITYnand3ISPORT（a，b，c：INSTD_LOGIC;y：OUTSTD_

2、LOGIC）;ENDnand3;ARCHITECTUREnand3_2OFnand3ISBEGINt4：PROCESS（a，b，c）VARIABLEcomb：STD_LOGIC_VECTOR（2DOWNTO0）;BEGINcomb：=a&b&c;CASEcombISWHEN“000”＝＞y＜＝‘1’;WHEN“001”＝＞y＜＝‘1’;WHEN“010”＝＞y＜＝‘1’;WHEN“011”＝＞y＜＝‘1’;WHEN“100”＝＞y＜＝‘1’;WHEN“101”＝＞y＜＝‘1’;WHEN“110”＝＞y＜＝‘1’;WHEN“111”＝＞y＜＝‘0’;WHENOTHERS＝＞

3、y＜＝‘X’;ENDCASE;ENDPROCESS;ENDnand3_2;二、编码器、译码器、选择器例：地址译码器假设一个微处理器存储空间为从0000H到FFFFH，将其分成5部分，它们的地址分配如下：0000H—DFFFH为动态随机存储器DRAM使用；E000H—E7FFH为I/O设备使用；E800H---EFFFH备用；F000H—F7FFH为第一个只读存储器ROM1使用；F800H—FFFFH为第二个只读存储器ROM2使用；其中选通控制信号DRAM1,IO,ROM1,ROM2均为低电平有效。例：地址全译码LIBRARYIEEE;USEIEEE.STD_LOGIC_1

4、164.ALL;ENTITYad_decoderISPORT(address:INSTD_LOGIC_VECTOR(15downto0);DRAM1,IO,ROM1,ROM2:OUTSTD_LOGIC);ENDad_decoder;ARCHITECTUREaOFad_decoderISBEGINPROCESS(address)BEGINIFaddress<=x”dfff”THENDRAM<=‘0’;IO<=‘1’;ROM1<=‘1’;ROM2<=‘1’;ELSIFaddress>=x”e000”ANDaddress<=x”e7ff”THENDRAM<=‘1’;IO<=‘0

5、’;ROM1<=‘1’;ROM2<=‘1’;ELSIFaddress>=x”f000”ANDaddress<=x”f7ff”THENDRAM<=‘1’;IO<=‘1’;ROM1<=‘0’;ROM2<=‘1’;ELSIFaddress>=x”f800”THENDRAM<=‘1’;I/O<=‘1’;ROM1<=‘1’;ROM2<=‘0’;ENDIF;EndPROCESS;ENDa;例：地址部分译码LIBRARYIEEE;USEIEEE.STD_LOGIC_1164.ALL;ENTITYad_decoderISPORT(A15,A14,A13,A12,A11:INSTD_LOG

6、IC;DRAM1,IO,ROM1,ROM2:OUTSTD_LOGIC);ENDad_decoder;ARCHITECTUREaOFad_decoderISBEGINPROCESS(A15,A14,A13,A12,A11)BEGINIF(A15ANDA14ANDA13)=‘0’THENDRAM<=‘0’;IO<=‘1’;ROM1<=‘1’;ROM2<=‘1’;ELSIFA12=‘0’ANDA11=‘0’THENDRAM<=‘1’;IO<=‘0’;ROM1<=‘1’;ROM2<=‘1’;ELSIFA12=‘1’ANDA11=‘0’THENDRAM<=‘1’;IO<=‘1’;R

7、OM1<=‘0’;ROM2<=‘1’;ELSIFA12=‘1’ANDA11=‘1’THENDRAM<=‘1’;IO<=‘1’;ROM1<=‘1’;ROM2<=‘0’;ENDIF;ENDPROCESS;ENDa;三、加法器、求补器例：半加器真值表二进制输入和输出进位输出basco0011010101100001例：8位二进制数的求补电路LIBRARYIEEE；USEIEEE.STD_LOGIC_1164.ALL；ENTITYhalf_adderISPORT（a，b：INSTD_LOGIC；s，co：OUTSTD_LOGIC）；E