Moeller LE 4-505-BS1, Hardware And Engineering

Page: 16 / 94

ASi System
14
02/98 AWB 27-1314-GB
installed. Slaves can have up to 4 inputs, 4 outputs
or 4 inputs and outputs. In each bus cycle, the
master reads the slave inputs, sets the slave outputs
or carries out both functions.
A four-bit data telegram is used to transport either
input or output data to the slaves.
Slaves with only two inputs and two outputs do not
use all four bits of each telegram. In this case,
unused inputs and outputs are transferred in the
telegram as empty bits.
In the PLC program, it is necessary to know the
position of the input and output bits within the four-
bit telegram in order to address them. This is
indicated by the slave’s I/O code, which is specified
with the slave profile (see following section for more
details).
Configuration parameters can be optionally
transferred to a single specified slave at the end of
each bus cycle. Configuration parameters can be
used to specify e.g. the operating distance of a
proximity switch.
The data is encoded using the Manchester II method
to ensure high reliability and high interference
immunity.
Due to the behaviour of the ASIC the unused input
bits 2 and 3 of the EM 2-205-DD1 are not set to “0”
but written with the inverted values of output bits 2
and 3. This applies to other devices using the same
ASIC if the bit numbers of the inputs and outputs do
not overlap.
H1314G.BK Seite 14 Freitag, 2. Juli 1999 9:02 09