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标题: @版主关于CRC的问题 [打印本页]

作者: reporter 时间: 2013-11-8 10:38 标题: @版主关于CRC的问题

本帖最后由 shxr 于 2013-11-8 08:22 编辑

下面是版主曾经在一篇帖子http://bbs.21ic.com/forum.php?mo ... 5&amp;page=1#pid3223407的回复。
我有些疑问，想请教版主。该程序适用于data为几位的情况。如果data为8位，则如何与crc1（0x6363）异或，高位扩展么？
data为16位的情况我已经验证过了，就是比较疑惑8位的情况。因为14443的CRC_A中没有给8为data的crc信息的例子，没法验证，求解惑。

“我去&nbsp;&nbsp;14443还分了CRC_A和CRC_B&nbsp; &nbsp;为什么要要搞两种啊&nbsp; &nbsp;刚仔细研究了一下&nbsp;&nbsp;给你计算出来了
他的初始值是0x6363&nbsp; &nbsp;我们以前计算初始值一般都是0xffff&nbsp; &nbsp;
还有计算不需要取反&nbsp;&nbsp;CRC_B和15693协议的计算方法是一样的&nbsp;&nbsp;
给你代码吧&nbsp;&nbsp;你看看
unsigned short crc16_ccitt(unsigned char data,unsigned short crc1)
{
&nbsp; &nbsp;&nbsp; &nbsp;&nbsp;&nbsp;unsigned short ccitt16 = 0x8408;
&nbsp; &nbsp;&nbsp; &nbsp;&nbsp;&nbsp;int i;
&nbsp; &nbsp;&nbsp; &nbsp;&nbsp;&nbsp;crc1 ^= data;&nbsp; &nbsp;/*新的数据与原来的余数（就是crc）相加（加法就是异或操作）*/
&nbsp; &nbsp;&nbsp; &nbsp;&nbsp;&nbsp;for(i=0;i&lt;8;i++)
&nbsp; &nbsp;&nbsp; &nbsp;&nbsp;&nbsp;{
&nbsp; &nbsp;&nbsp; &nbsp;&nbsp; &nbsp;&nbsp; &nbsp;&nbsp; &nbsp; if(crc1 &amp; 0x0001)&nbsp;&nbsp;/*最低位为1，减去除数 */
&nbsp; &nbsp;&nbsp; &nbsp;&nbsp; &nbsp;&nbsp; &nbsp;&nbsp; &nbsp; {
&nbsp; &nbsp;&nbsp; &nbsp;&nbsp; &nbsp;&nbsp; &nbsp;&nbsp; &nbsp;&nbsp; &nbsp;&nbsp; &nbsp;&nbsp; &nbsp;crc1 &gt;&gt;= 1;
&nbsp; &nbsp;&nbsp; &nbsp;&nbsp; &nbsp;&nbsp; &nbsp;&nbsp; &nbsp;&nbsp; &nbsp;&nbsp; &nbsp;&nbsp; &nbsp;crc1 ^= ccitt16;
&nbsp; &nbsp;&nbsp; &nbsp;&nbsp; &nbsp;&nbsp; &nbsp;&nbsp; &nbsp; }
&nbsp; &nbsp;&nbsp; &nbsp;&nbsp; &nbsp;&nbsp; &nbsp;&nbsp; &nbsp; else&nbsp; &nbsp;&nbsp; &nbsp;&nbsp; &nbsp;/*最低位为0，不需要减去除数 */
&nbsp; &nbsp;&nbsp; &nbsp;&nbsp; &nbsp;&nbsp; &nbsp;&nbsp; &nbsp; {
&nbsp; &nbsp;&nbsp; &nbsp;&nbsp; &nbsp;&nbsp; &nbsp;&nbsp; &nbsp;&nbsp; &nbsp;&nbsp; &nbsp;&nbsp; &nbsp;crc1 &gt;&gt;= 1;&nbsp;&nbsp;/*直接移位*/
&nbsp; &nbsp;&nbsp; &nbsp;&nbsp; &nbsp;&nbsp; &nbsp;&nbsp; &nbsp; }
&nbsp; &nbsp;&nbsp; &nbsp;&nbsp;&nbsp;}
&nbsp; &nbsp;&nbsp; &nbsp;&nbsp;&nbsp;return crc1;
}

int main()
{
&nbsp; &nbsp;&nbsp; &nbsp;&nbsp;&nbsp;int i ;
&nbsp; &nbsp;&nbsp; &nbsp;&nbsp;&nbsp;unsigned short crc;
&nbsp; &nbsp;&nbsp; &nbsp;&nbsp;&nbsp;char data[11] ={0x00,0x00};
&nbsp; &nbsp;&nbsp; &nbsp;&nbsp;&nbsp;crc = 0x6363;
&nbsp; &nbsp;&nbsp; &nbsp;&nbsp;&nbsp;for(i=0;i&lt;2;i++)
&nbsp; &nbsp;&nbsp; &nbsp;&nbsp;&nbsp;{
&nbsp; &nbsp;&nbsp; &nbsp;&nbsp; &nbsp;&nbsp; &nbsp;&nbsp; &nbsp; crc = crc16_ccitt(data,crc);
&nbsp; &nbsp;&nbsp; &nbsp;&nbsp;&nbsp;}
//&nbsp; &nbsp;&nbsp; &nbsp;&nbsp;&nbsp;crc = ~crc;
&nbsp; &nbsp;&nbsp; &nbsp;&nbsp;&nbsp;printf(&quot;crc is %x&quot;,crc);
&nbsp; &nbsp;&nbsp; &nbsp;&nbsp;&nbsp;return 0;
}
”

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