CAN×????????·???à???é???????í?°?????·????  
????×÷???????é?? ?? ?÷ ???ú??


   ????????CAN???????????????±?????ù?????ò???????????ò???ù?ù??????????????±¨???????í?????????°?±??????°?±¨??????????·??????§???ì???í?ó???è?????????í???????ê???é????CAN×????????·???à???é???????í???????í?°??????·?·¨??

   ???ü???????·???à???é ???í???? ±¨??

??CAN????????±??¤±¨???????????·?????è?????¨?????????????í?????????°??????·?·¨??·?????·???????????????????·????????í??????·?????±?×?????·??????±?????í???????è???ì?í?????????????ì?í?????à?????????é???????·???à???é???????????é????????×????????ì?í??????????·?·¨?ò???????ì?í?????????????·???à???é????±à???????ò?????ó?????????ù?????¨????????????????·??????????????é??CAN?????????·???à???é???¨??CRC?????????í??????·?·¨??


[???ù±?zona??2004-05-21 10:55 PM????±à??]

1 CRC???ì?í???¤×÷???í

CRC???ì?í????±????í±¨????±????ò???±×÷???????????à????A?¨x????????????????????·???·???????·??¤?????¨?????ú???à????g(x)?ó?????ó?????à??P(x)×÷??CRC???é??????????????±¨????????????·???????·???????·??????ù??g(x)??????????±¨??B(x)???????à??????p(x)???ò???????ó?¨???±A?¨x????B(x)?à??????·??ò?????????????í????·???????·???????????CRC???é???±?????ó??????

???????é?????????????è×?????????????CRC?????±?????????????¨??2??????·¨??????·¨??????????·¨???è??????±?????????????×÷???????????ì?ò??????????????CRC?????°????·???±¨???ù±í?????à????A(x)????xn??????n???ú???à????g(x)??×???????????????????·¨??????A(x)?¤xn??????A(x)×ó??n??????????·??à??p?¨x?????ù??????·?????±¨????±???A?¨x???¤xn+p(x)?????ú???à????g(x)???×????×??ó??????????±?????1??

??1??CRC???é???¤×÷??????

???°???????à???ú???à????±??????ú??±ê×?????????CRC-4??CRC-12??CRC-16??CCITT-16??CRC-32????CAN×????????????ú???à??????g(x)=x15+x14+x10+x8+x7+x4+x3+1????????????CANU????????CRC???é???????à???????????é??????±???°?CRC???é?¨CRC-4??CRC-12??CRC-16???????????¨???????????????í?à???ò???ü???ì?í???????????ó???????????????á???????????????????§?ì?í??????

2 CRC???????·????

2.1 ???????·??????

??CAN×??????????ú?úCRC???????????·???????????????±???????????????è??????????????????????????????????????????destuff???ü?????§????????1????CRC?ì?é??????????enable?????§????????1???????????·?????????????????÷??·??à?÷?ú???????è?????????ì?ò????????????±??????????????????ú?ú??±??????±?????¤???????á?????????????è?????·??

2.2 ???????·??

??2????????CRC???????????·????

?????è?????÷??????????????????????????????????????????????crcnxt?ú±í??????????????±¨???ò????CRC?????÷??×??????ì?ò???á??????±ê??0??14?ù????????15??CRC?????÷??????????·?????±ê??1??6?ù?????????????÷??·??à?÷??×é?????????????ì?ò?????????????÷????????????Y=AB+AC???????á??????3?ù????

2.3 ???·?¤×÷????

??????·????????????±enable=0?±??CRC??0?????±enable=1??destuff=1?±??????????CRC?????????±enable=1??destuff=0?±???????????????±????????????????

???÷???????????ù???§?±??????±¨????????????????CRC?????÷??×??????à?ì???ó????×??????????±?????÷????13??9??7??6??3??2???ù????×??????ì?ò???á??·?±?×ó???????????ü???????ì?ò??×÷???????÷??????·?±?×ó?????????±??±¨????????????????CRC?????÷?????????±?????÷????????????????????CRC????

????±¨????±????ò???¤????16???ò?è??×ó??16????????±¨???????????ù???????í????????Ck±í??CRC?????÷????k????????Ck&#39±í???????ó????k???????¨k=0,1,2,3????15?????ò??????????±í1??

3 CRC???é?????í??????

CRC???é???í??????????·???·?±??????????°??×??????é????·?·¨?à????C????????±à???????????????±·????????è????????????????????CRC????Verilog HDL?????????è?????ò??

±????ò??Verilog_XL??±à???¨???????±??Synopsis????????????×????°??????

//??Verilog HDL????CRC??

module crc(clk,rst,enable,destuff,datain,crc)??

input clk;

input rst;

input enable;

input destuff;

input datain;

output[14:0]crc;

reg[14:0]crc;

wire crcnxt=datain^crc[14];

always@(posedge rst or posedge clk)

begin

if(rst)crc=0;

else if(enable && destuff)

begin

if(crcnxt)

crc<=crc^15h񠕧

else

crc<={crc[13:0],1&#39b0};

end

end

endmodule

4 ·????¨??

???è·???????????±ê×????????????????è?ó??????×?????8??±ê??·??ò????10101011000???ò?????????ò·????ó???¨??????4?ù????Crc?ò??????20????????????

CRC???é?????ì?í??????????????????CRC???ì?í???í?????????????????ò?????ò??±???·??????????÷?à???????é????CRC???ì?í???á???????????????????§?ì?í????????????