BECKHOFF BC3100 - Manual (Page 15)

Basic information
BC3100 15
length of the area to be mapped can be set by way of the configuration
interface. As the terminal signals are placed into the process image of the
PLC task as from address zero, the first meaningful offset as from when
inputs and outputs of the PLC task are mapped into the field bus process
image is the first free address where there are no longer any terminal
signals.
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.
Commissioning and diagnostics
After power on, the bus terminal controller immediately checks the
connected configuration. Error-free start up is signalled by virtue of the fact
that the red "I/O ERR" LED goes off. When it flashes, the "I/O ERR" LED
indicates an error in the area of the terminals. The error code can be
determined by the frequency and number of flashes. This enables swift
troubleshooting.
The diagnostic LEDs The bus terminal controller has two groups of LEDs to provide a status
display. The top group consisting of four LEDs indicates the status of the
respective field bus. The meanings of the "field bus" status LEDs are
explained in the corresponding chapters of this manual. They correspond
to the usual field bus displays.
There are two further green LEDs on the top right hand side of the bus
terminal controller to indicate the supply voltage. The left hand LED
indicates the 24 V power supply of the bus terminal controller. The right
hand LED signals the power supply of the Power contacts.