NDC BETA LaserMike LaserSpeed Pro 8500-4, Instruction Handbook Manual

Page: 274 / 348

11-8 LaserSpeed Pro 8500-4 Instruction Handbook:
Profibus DP™
11.3.8 PKW Write Float (Command Code 7)
This command allows a floating-point database item to be written.
The Profibus master specifies the database item identifier within the command qualifier. If the referenced
database item is not floating point, then the response code will be set to “wrong type.”
The contents of the PKW Request Data are treated as a 32-bit floating-point number to be written in to the
database, and the PKW Response Data will be all zeroes.
11.3.9 PKW Load String (Command Code 8)
Since only four data bytes are available for communicating information within the PKW header, it is necessary
to load a string into a temporary buffer from where it can be read four bytes at a time. The PKW Load String
command performs this function.
The Profibus master specifies the database item identifier within the command qualifier. If the referenced
database item is not a string, then the response code will be set to “wrong type.”
The gauge sets the PKW response data to the length of the string. This length indicates the number of non-
null characters within the string. The Profibus master can use this length to determine how many Read String
Segment requests must be issued, or to pre-allocate a buffer for receiving string data, etc. It is also possible
to detect the end of string when reading the string segments, so the string length within the response data
may be ignored if its use is not required.
11.3.10 PKW Read String Segment (Command Code 9)
This command allows a Profibus master to read segments of a string that has previously been loaded into a
temporary buffer using the Load String command. The string can be read 4 bytes at a time.
The Profibus master specifies a string segment number in the command qualifier field. The string segment
number starts at 0, then works up incrementally 1, 2, 3, etc. It is not necessary to read the segments in any
particular order, although if the size of the string supplied in response to the Load String command has not
been retained then it is recommended that segments be read in ascending order so that the operation can be
terminated when the null-terminator is detected.
The gauge always responds with 4 bytes in ascending order within the PKW Response Data area. For a
string segment number N, the returned characters are from a starting index position N*4 within the temporary
string buffer. Attempts to read beyond the end of the temporary string buffer will return all zero data.
The gauge always provides at least one null terminator byte after the string data (assuming the master reads
sufficient string segments). If the temporary buffer has previously been used to load other strings, then non-
null data may follow the first null terminator byte. The Profibus master should detect and use the first zero
byte as a null terminator.