48 Unidrive M SI-PROFIBUS User Guide
Issue Number: 3
8 Cyclic data
8.1 What is cyclic data?
Cyclic data transfer is a method of transferring data on a regular time period, often
known as ‘polled data’. High-speed data transfer is achieved by transmitting only data
bytes over the PROFIBUS-DP network and using local mapping information within the
SI-PROFIBUS and PROFIBUS-DP master controller to ensure that the correct data is
sent to the correct locations. The flexibility of the SI-PROFIBUS means that each cyclic
data OUT channel can be directed to any read/write drive parameter. Similarly each
cyclic data IN channel can use any drive parameter as a source of data.
See section 8.7 Master configuration on page 51 for more information regarding the use
of data alignment with 16-bit parameters.
8.2 Data formats
The SI-PROFIBUS can be configured with up to sixteen 32-bit or thirty-two 16-bit cyclic
IN and OUT data words. IN and OUT cyclic data words are mapped using up to 32
mapping (pointer) parameters, one for each mapping.
In addition to cyclic data, non-cyclic data (see section 9 Non-cyclic data on page 52)
exchange is also possible by the following methods:
• DP-V1 parameter access mode
• Mode 1 - CT Single Word
• Mode 2 - PPO 4 Word
The method used to map cyclic data to and from the PROFIBUS-DP network is similar
to the method used in the drive for mapping analog and digital I/O. The reference for the
source or target parameter is entered in the mapping parameter in the form mm.ppp,
where:
mm = menu number of the target/source parameter
ppp = parameter number of the target/source parameter.
• The term OUT data refers to data that is transmitted out of the master to the
slave.
• The term IN data refers to data that is returned from a slave into the master.
• Cyclic data mapping cannot be changed dynamically, as changes to the
configuration (mapping parameters, etc.) will only take effect during
initialization of the SI-PROFIBUS.
• The maximum number of 16-bit mappings that is possible is 32 with only
cyclic data, this requires data alignment to be set to 16, see for more
information.
• The maximum number of 32-bit mappings that is possible is 16 with only
cyclic data.
By default all drive parameters are cast as 32-bit (two 16-bit words) therefore thirty-two
cyclic words gives sixteen possible drive parameters. Data alignment reduces the
number of cyclic words required for drive parameters of 16-bit (or less) to 16 bits thus
allowing for thirty-two possible 16-bit parameters. Any 32-bit parameters mapped will
still require two 16-bit words even with alignment set to 16.
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