BECKHOFF BK7000 - Manual (Page 14)

Basic information
13 BK 7000
Analog inputs/ouputs are representative of other complex multi-byte signal
bus terminals (RS232, SSI sensor interface, ...)
Overview of the subdivision of the process image in the bus coupler:
Output data in the
bus coupler
O0
...
byte-oriented data
...
Ox
Ox+1
bit-oriented data
Ox+y
Input data in the
bus coupler
I0
...
byte-oriented data
...
Ix
Ix+1
...
bit-oriented data
...
Ix+y
Data consistency
Data which contains no contradictions is said to be consistent. The follow-
ing consistency is required here: 1. The high byte and low byte of an ana-
log value (word consistency), 2. The control/status byte and the corre-
sponding 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 sys-
tems guarantee consistency to the required length. It is important to use
the appropriate procedure for importing this consistent data from the mas-
ter 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 par-
ticular 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 dif-
ference 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 selec-
ted directly from the "GSD file". The configuration software automatically
ensures the settings for maintaining data consistency.