46 Unidrive M SI-PROFIBUS User Guide
Issue Number: 3
7 GSD Files
7.1 What are GSD Files?
GSD files are text files that are used by the PROFIBUS-DP network configuration
software tools. They contain information about the device timings, supported features
and available data formats for the SI-PROFIBUS device. Drive icon files are also
supplied for use with the SI-PROFIBUS configuration software. GSD files are available
from your supplier, local Control Techniques Drive Centre or the Control Techniques
website (www.controltechniques.com).
7.2 Data consistency
There is a potential problem with data skew when transferring blocks of data to and from
a PROFIBUS-DP master controller. Data skew happens when a value is spread across
multiple words; when this occurs it is possible that only half of the correct value reaches
the destination. Consider the following example:
• The PLC has a value of 0xFFFFFFFF to send to the drive.
• The drive currently has a value of 0x00000000 in a 32-bit parameter.
• The master controller sends the word without consistency.
• The drive receives one 16-bit word and now has the value 0x0000FFFF.
• The drive receives the next 16-bit word and now has the value 0xFFFFFFFF.
To prevent data skew PROFIBUS-DP has a feature known as ‘data consistency’.
Consistent data defines a block of data words that must ALL be updated before ANY of
the new data values are transmitted. Consequently, the message sent over the
PROFIBUS-DP network will have a true representation of the required data. Some
PLCs have special functions available to transfer blocks of consistent data to a
PROFIBUS-DP master controller and guarantee that data skew cannot occur.
7.3 Data configuration
The GSD file describes the modules of input or output words that may be combined to
configure the input and output configuration for a specific node. The complete input and
output configuration for the node is built by adding the required modules until all of the
node’s inputs and outputs are defined.
The number of input or output words configured in the drive must match the number of
input or output words defined in the master controller; if the master has eight IN and four
OUT words the drive must use the same settings to communicate correctly.
The SI-PROFIBUS module uses Pr S.01.020 and Pr S.01.021 to independently set the
number of input and output words respectively.
A module consists of a block of input or output data. Put simply this is a logical collection
of data words.
The definition of a data word is 16 bits. By default SI-PROFIBUS casts all data as long
words/double words (32 bits), data alignment can be used to reduce this size, see
section S.01.014 on page 35 for more information.
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