4-8
ET 200U Distributed I/O Station
EWA 4NEB 812 6087–02b
If an input/output value is read in via the process I/O image, the following
conditions may result:
Assumption: Failure of station 1 in the PII or in the PIQ
The CPUs 941 to 944 detect a failure of station 1 since they read in/write the
process I/O image word–by–word. Therefore, the CPUs do not read/write
address 0 in the process I/O image of station 2, although station 2 is avail-
able.
The CPU stops with timeout (if in COM ET 200 “timeout = yes”). After a
transition from STOP to RUN, the CPU switches again to RUN. Station 1 and
address 1 of station 2 are not entered in the process I/O image.
Assumption: Failure of station 2
PII: The CPUs 941 to 944 detect a failure of station 2 since they read in the
process I/O image word–by–word.
The CPU stops with timeout (if in COM ET 200 “timeout = yes”). The CPU
remains in the STOP mode even after a transition from STOP to RUN.
PIQ: The CPUs 941 to 944 detect a failure of station 2 since they read in/
write the process I/O image word–by–word. Therefore, the CPUs do not
read/write address 0 in the process I/O image of station 1, although station 1
is available.
The CPU stops with timeout (if in COM ET 200 “timeout = yes”). After a
transition from STOP to RUN, the CPU switches again to RUN. Station 2 and
address 0 of station 1 are not entered in the process I/O image.
Note
To avoid the above conditions, note the following when addressing CPUs
941 to 944:
1. Use load and transfer commands. These commands work on a byte–by–
byte basis and are thus able to identify the presence of each individual
byte.
2. Assign an even number as address start in a slave station (e.g. 0, 2, 4, 6,
...) and do not use the uneven address numbers. This enables you to ac-
cess the process I/O image.
Example division of the digital and analog I/O areas:
1. Accept “0” as the next available address for DI and DQ modules.
2. Enter “128” as next available address for AI and AQ modules.
This division corresponds to the usual SIMATIC division of the P area. How-
ever, you can separate the areas according to your needs.
Condition 1
Condition 2
Example Division
of the Digital/Ana-
log I/O Areas
ET 200U(DP Siemens): Address Assignment,Starting–Up,Diagnosing Faults Using COM ET200