BECKHOFF BK7500 - Manual (Page 16)

Basic information
16 BK7500
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 or word: the
bits which make up a byte or a word 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.
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.