BECKHOFF BK3000 - Manual (Page 17)

Basic information
BK3xxx/LC3100 17
The path from the I/Os to
the PROFIBUS process
image
Data consistency Data which contains no contradictions is said to be consistent. The
following consistency is required here: 1. The high byte and low byte of an
analog value (word consistency), 2. The control/status byte and the
corresponding parameter word for accessing the register. The interaction
of the peripherals with the control unit means that data can initially be
guaranteed consistent only within an individual byte: the bits which make
up a byte are read in together, or written out together. Byte-wise
consistency is quite adequate for processing digital signals but is not
sufficient for transferring values longer than eight bits, such as analog
values. The various bus systems guarantee consistency to the required
length. It is important to use the appropriate procedure for importing this
consistent data from the master bus system to the control unit. You will find
a detailed description of the correct procedure in the User Guide of the
appropriate bus system, in particular in the description of the standard
master units that are installed. The chapters of this manual which deal with
the fieldbus refer to the most common of these standard units.
Processing complex signals All byte-oriented signal channels such as RS232, RS485 and incremental
encoder, can use byte lengths greater than two. Apart from the actual
difference in length, the procedure is always comparable with that for
analog signals. In the configuration software for the bus masters of the
second generation (from around 09.96), the corresponding channel can be
selected directly from the "GSD file". The configuration software
automatically ensures the settings for maintaining data consistency.