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

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LaserSpeed Pro 8500-4 Instruction Handbook:
Profibus DP™
11-9
11.3.11 PKW Write String Segment (Command Code 10)
Since only four data bytes are available for communicating information within the PKW header, it is necessary
to build a string within a temporary buffer from where it can be written into the database. The PKW Write
String Segment command performs this function.
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. For a string segment N, the gauge then copies
the four supplied string bytes (possibly containing a null terminator) from the PKW Request Header into the
temporary buffer at index position N*4. It then adds a null terminator to the temporary buffer at index position
(N+1)*4. This defensive technique means that the temporary buffer is always null terminated, regardless of
the order in which data is received from the master. It is therefore not necessary for the master to supply a
null terminator if the string length is an exact multiple of four bytes. However, the technique requires string
segments to be written in ascending numerical order.
If the previous PKW command was not to write a string segment, then the gauge inserts a null terminator at
the start of the temporary buffer. Therefore, all Write String Segment commands and the following Save
String command must be sent contiguously.
If the specified string segment N is valid, then the gauge reflects the supplied PKW request header string data
within the PKW Response Data. If the specified string segment N is not valid, then the gauge sets all PKW
Response Data bytes to all zeroes.
11.3.12 PKW Save String (Command Code 11)
A string previously loaded into the temporary string buffer using the Write String Segment command is written
to the LaserSpeed Pro database using the Save String command.
The Profibus master specifies the database item identifier within the command qualifier. If the referenced
database item is no
t a string, then the response code will be set to “wrong type.”
The immediately preceding command must have been a Write String Segment, otherwise a No String re-
sponse code is generated. This is a defensive mechanism to help prevent accidentally writing zero length or
invalid strings into the database.
The gauge sets the PKW Response Data to all zeroes.
11.3.13 PKW Measurement Enumeration (Command Code 12)
This command allows the LaserSpeed Pro measurement table to be enumerated. A single measurement
item can be enumerated with each command/response exchange; this makes it quite slow to enumerate the
entire measurement table. There is no requirement to enumerate the measurement table. The measurement
table section of this document provides details of measurements item identifiers, types, and access permis-
sions, and it is possible to use this published information directly with the other measurement table services.
The enumeration service allows generic test programs to be written that have no prior knowledge of the La-
serSpeed Pro measurement table.