实现HDB3编码，HDB3码是AMI码的一种改进型，其目的是为保持AMI码的优点而克服其缺点，使连“0”个数不超过3个。-Achieve HDB3 encoding, HDB3 code is a modified AMI code, its purpose is to maintain the benefits of AMI code to overcome its shortcomings, so that even the " 0"　the number of not more than 3.