Gsd Files; What Are Gsd Files; Data Consistency - Leroy-Somer digitax st User Manual

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GSD Files

6.1

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 PROFIBUS-DP device. Drive icon files are also
supplied for use with the PROFIBUS-DP configuration software. GSD files are available
from your supplier, LEROY-SOMER or the LEROY-SOMER website (www.leroy-
somer.com).
6.2

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 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.
6.2.1 Limitations of non-cyclic data Mode 1 - CT Single Word with GSD
CT Single Word non-cyclic data uses only 1 word of data, however when used without
data compression (see section 12.5 Cyclic data compression ) this requires two 16-bit
words (a single 32-bit word). When used without compression only the lower 16-bits of
the 32-bit word are used.
6.2.2 Using non-cyclic data Mode 2 - PPO 4 Word
Data consistency is important when using PPO4 word (Mode 2) non-cyclic data as each
non-cyclic message consists of four words. If there is data skew between any of the
non-cyclic words this could result in the wrong data value being written to the wrong
parameter.
The GSD file provides the PPO 4 Word which consists of four IN/OUT words with
consistency.
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SM-PROFIBUS DP-V1 User Guide
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