IM151-1 HIGH FEATURE interface module (6ES7151-1BA02-0AB0)
Manual, 03/2008, A5E01075975-02
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Functions
3
3.1
Cycle synchronization
3.1.1
Basics
Properties
Reproducible response times (i.e., of equal length) are achieved in SIMATIC with a constant
DP bus cycle, synchronization of the user program on the DP bus cycle, and the isochronous
transfer of I/O data to the I/O modules. The isochronous sections of the user program are
processed synchronously with the DP bus cycle by means of synchronous cycle interrupts
(OB 61 to OB 64). The I/O data are transferred at defined and constant (isochronous)
intervals via the backplane bus of the DP slave to the I/O modules and switched through
isochronously up to the "terminal".
In other words, isochronous operation results in the synchronization of all hitherto free-
running single cycles. These include the user program in the CPU, the DP cycle on the
PROFIBUS subnet and the cycle in the DP slave right up to the cycle in the I/O modules of
the DP slaves.
The maximum jitter for the IM151-1 is 10 µs. The jitter of the ET 200S I/O modules cannot be
considered due to the existing diversity.
Requirements
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Cycle synchronization is possible with the IM151-1 HIGH FEATURE with modules which
support cycle synchronization. You can see whether a module supports cycle
synchronization in the device description or HW Config. Other modules can be used in
the ET 200S setup, but they do not support cycle synchronization.
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The transmission rate of the PROFIBUS DP is at least 1.5 Mbps (shorter equidistance
times can be achieved with higher transmission rates).
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The maximum constant bus cycle time is 32 ms.
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The constant bus cycle time master (class 1) must be a class 1 DP master. This means a
programming device/PC cannot be a constant bus cycle time master.
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Only one DP master (class 1) may be active on the PROFIBUS DP during equidistant
mode. Programming devices or PCs (class 2) can also be connected.
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The isochronous mode can only be activated on the ET 200S if the constant bus cycle is
enabled on the DP master system.
●
Isochronous operation (constant bus cycle time) of the ET 200S is not possible during
removal or insertion of electronic modules.
In order to ensure that asynchronous results such as "Switch on power module" or
"Read/Write data record" do not cause cycle violation, a sufficiently large gap between To
and Ti must be provided, i.e. Tdp must be increased.
