IEC 61334-6:2000 pdf free download – Distribution automation using distributionline carrier systems
6 Encoding procedures
6.1 Encoding of an INTEGER value
A-XDR provides two types of encoding for the ASN.1 INTEGER type, depending on whether theASN.1 definition of an iNTEGER is value-constrained or not. When an lNTEGER is specified tobe within a restricted range of values，for example INTEGER(-128..127), it is encoded asa fixed-length integer.Otherwise,when no range is specified, the INTEGER is encoded as avariable-length integer.
6.1.1 Encoding of a fixed-length integer value
Two different encodings are provided by A-XDR for fixed-length integers: integers which arespecified to be within a non-negative value range are represented and encoded as unsignedbinary numbers，while integers which may take negative values are represented and encodedas two’s complement binary numbers. ln both cases,only the value of the integer is encoded,forming the contents field of the encoding.The aim is to provide minimal-length encoding.
6.1.1.1 Encoding of fixed-length, unsigned integer values
When an INTEGER is specified to be within a non-negative value range, it is encoded as anunsigned binary number. The number of bytes of the encoding is determined by the specifiedvalue-range: it is equal to the minimum ‘number of necessary bytes which is required torepresent any value within the specified range.The range of a fixed-length unsigned integer isalways aligned on byte boundary.
6.1.1.2 Encoding of fixed-length, signed integer values
When an INTEGER is specified to be within a value range which includes negative values, it isencoded as a two’s complement binary number.The number of bytes of the encoding isdetermined by the specified value-range; it is equal to the minimum number of necessary byteswhich is required to represent any value within the specified range.The range of a fixed-lengthinteger is always aligned on byte boundary.
Encoding of a non-constrained INTEGER value when it is out of the above 0 s value <128range contains two fields: the first,fixed-length field – Length – represents the length of thesecond, variable-length field, in bytes.This second, variable-length field -Contents – conveysthe encoded value, and contains an integral number of bytes.
The Length field is encoded in one byte11), with bit 8 set to 1 (indicating the presence of theLength field). The remaining seven bits are encoded as a fixed-length,unsigned integer,，thevalue of which represents the number of bytes in the contents field.
The number of bytes of the encoding is determined by the value to be encoded: it is equal tothe minimum number of necessary bytes which is required to represent the given value.
The encoding of the value is a two’s complement binary number equal to the integer value, andconsists of bits 8 to 1 of the first byte，followed by bits 8 to 1 of the second byte,followed bybits 8 to 1 of each byte in turn, up to and including the last byte of the encoding – as specifiedalso for fixed-length，signed integers (6.1.1.2). The structure of a variable length integerencoding is shown in figure 4.
6.2Encoding of a BOOLEAN value
A BOOLEAN type may take only two values: it is either TRUE or FALSE.A-XDR encoding of aBOOLEAN value contains only the Contents field, which consists of one byte. lf the value to beencoded is FALSE, this byte is zero (all bits are zero), otherwise – when the value is TRUE -this byte can be any non-zero value, as a sender’s option.