21
of 175
In general, retrieving 240 bytes from a slave is too long for the user because it makes the total cycle
time too long. This is why different modified response lengths (see chapter 6.1 Meaning of the
contents of the different protocol modes on page 23) are provided in the DIGIFORCE
®
9307 unit.
PROFIBUS DPV1 data transfer
With PROFIBUS DPV1, a master can use acyclic bus access to access individual device parameters,
retrieve them or write new values for the parameter.
DIGIFORCE
®
9307 supports DPV1 access for complete device configuration, evaluation and
measurement data.
Further information
The PROFIBUS and PROFINET International (PI) provides additional documents on the Internet:
5.2 General information on PROFIBUS data transfer
For PROFIBUS DP (cyclic data traffic), one must define at the configuration stage how many bytes are
transferred between master and slave during each cyclic access (GSD file).
The device is controlled using the data transferred from master to slave. This data always consists of
four bytes for the DIGIFORCE
®
9307 unit. The function of these four bytes is explained in chapter 6.2
PLC inputs - Transfer from master to slave.
The data transferred in the opposite direction from slave to master contains status information and
measurement results. Since the DIGIFORCE
®
9307 is a highly complex piece of test equipment, there
is an extremely large amount of data that could be transferred in this case. This is not always practical
however. For example, if one is only interested in the status information, it makes little sense to
transfer more than 100 bytes of measurement results per access which the master makes no use of.
On the other hand, there are applications in which the measurement results from a specific evaluation
element need to be transferred; but this would not be possible if only the status information per
interface is available
Hence in order to satisfy as many customer requirements as possible, 5 different combinations of
different measurement results have been provided. These different options specify what information is
sent to the master. The information content of the individual options ("modes") ranges from a simple
short message (e.g. mode 1 contains just PLC status and evaluation information; just 8 bytes are sent
to the master in this case) to complex longer messages containing a large amount of information (e.g.
mode 5 contains PLC status and evaluation information and 30 measurement values which are user
selectable within the 9307 configuration and the live values of max. 3 active measurement channels;
140 bytes are sent to the master in this case). When designing the system, the user can select the
option that best meets his requirements so that he receives precisely the data that he needs.
5.3 GSD file
DIGIFORCE
®
equipment with the PROFIBUS option is supplied with a CD. This disk includes the
device description file BUR_0D0D.gsd (GSD file). This GSD file describes the physical properties of
the device (baud rate, specific bit times, sent/received bytes per cycle etc.).
The structure, contents and encoding of this device description data is standardized so that any DP
slaves can be configured using configuration tools from various manufacturers.
The GSD file does not specify what data is transferred or how this data should be interpreted. The
user must glean this information from the operating manual and program his master accordingly.
