Siemens SIMATIC S7-1500 System Manual page 217

Special features in program execution
• You create the user program for the S7‑1500R/H redundant system in the top CPU (for
example PLC_1) in the STEP 7 project tree.
• The S7‑1500R/H redundant system does not support some of the instructions the S7‑1500
CPUs. Instructions that are not supported by the S7‑1500R/H redundant system are grayed
out in STEP 7 in the "Instructions" task card.
STEP 7 shows the instructions that are not supported in the program code in red. If you
compile program code with instructions that are not supported, STEP 7 outputs an error
message.
The instructions that are not supported are set out in the section Restrictions (Page 217).
• In the case of instructions with the "LADDR" block parameter, you use this parameter to
determine which of the two CPUs is the target of this instruction.
Example: To read out the I&M data of the CPU with redundancy ID 1, specify the HW
identifier 65149 (or the "Local1" system constant) at the "LADDR" block parameter of the
Get_IM_Data instruction.
You can find more information about the block parameters and the system constants of
the S7‑1500R/H redundant system in the STEP 7 online help.
• In the case of a SYNCUP, the execution time of many instructions operating
asynchronously is extended. If you call asynchronous instructions in SYNCUP system state
with the redundant S7-1500R/H system, the required function may not be triggered.
Solution: After SYNCUP ends, call the asynchronous instruction again. The function will
then be triggered.
Recommendation: Always call the asynchronous instructions cyclically.
• In contrast to the S7-1500 automation system, the redundant S7-1500R/H system
initializes temporary local data for functions (FCs) not only during optimized block access
but also during non-optimized block access. Information on system initialization for
optimized block access can be found in the STEP 7 online help.
• Changing CPU settings with data records for the SNMP status and the behavior in case of
faults of the acyclic communication (for example with the instructions RDREC and WRREC):
If you want to change the default behavior of the CPU for the specified application cases
per data record transfer, the following special data records are available to you for this
purpose. The structure of the data records is identical for standard and R/H-CPUs.
However, when programming in the context of redundant systems, particular points have
to be taken into consideration so that the setting acts on both CPUs. These particular
points are specified in the corresponding sections of the PROFINET and Communication
function manuals:
– Communication (https://support.industry.siemens.com/cs/ww/en/view/59192925)
– PROFINET (https://support.industry.siemens.com/cs/ww/en/view/49948856) function
Programming style guide
The programming guidelines described in the programming style guide help you to create a
uniform program code. You can better maintain and reuse the uniform program code. This
allows you to detect or avoid errors early on, for example, through compilers.
The programming style guide is available on the Internet
(https://support.industry.siemens.com/cs/ww/en/view/109478084).
S7-1500R/H redundant system
System Manual, 11/2022, A5E41814787-AD
function manual: SNMP
manual: Handling timeouts while exchanging data
Basics of program execution
9.1 Programming the S7-1500R/H
217