异步复位8421码十进制计数器vhdl.doc

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1、异步复位8421码十进制计数器：LIBRARYIEEE;USEIEEE.STD_LOGIC_1164.ALL;USEIEEE.STD_LOGIC_UNSIGNED.ALL;ENTITYBCDcoderISPORT(cp,clear:INSTD_LOGIC;q:OUTSTD_LOGIC_VECTOR(3DOWNTO0));ENDBCDcoder;ARCHITECTUREaOFBCDcoderISSIGNALtemp:STD_LOGIC_VECTOR(3DOWNTO0);SIGNALtmp:INTEGERRANG

2、E0TO49999999;SIGNALclk_out:STD_LOGIC;BEGINP1:PROCESS(cp)BEGINIFcp'eventANDcp='1'THENIFtmp=49999999THENtmp<=0;ELSEtmp<=tmp+1;ENDIF;IFtmp<=24999999THENclk_out<='0';ELSEclk_out<='1';ENDIF;ENDIF;ENDPROCESSP1;P2:PROCESS(clear,clk_out)BEGINIFclear='1'THENtemp<="0

3、000";ELSIF(clk_out'eventandclk_out='1')THENIFtemp="1001"THENtemp<="0000";ELSEtemp<=temp+1;ENDIF;ENDIF;ENDPROCESSP2;q<=temp;ENDa;