Siemens S7-300 Configuration Manual page 49

Option / input area
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Configuring and commissioning S7 CPs for Industrial Ethernet
Configuration Manual, 09/2013, C79000-G8976-C182-13
Multiplex OP connections /
Occupy internal CPU
connection resource
Disable UDP frame buffering With this option, you can choose between the following reactions:
Configuring the Ethernet CP with STEP 7
Meaning / effect
To connect TD/OPs and/or HMI devices, you can optimize the
connection resources in the S7-300 CPU by allowing up to 16 such
devices to communicate on a single CPU connection resource
(multiplex mode).
If you do not use this option, the number of TD/OPs and/or HMI
devices that can be used will depend on the number of available
connection resources of the CPU used.
As default, this option is deactivated. This means that a CPU
connection resource is used for multiplex only when necessary.
Configured S7 connections over the CP use the same multiplex
channel as you use for multiplexing the HMI connections. If you
configure S7 connections, this means that one CPU connection
resource is already used.
Please note: PG connections are not operated over the
multiplexer. When operating a PG, a connection resource is
always occupied.
Note on programming:
When you use the multiplex mode, specify the rack/slot
assignment of the CP for addressing on TD/OP/HMI connections
instead of the rack/slot assignment of the CPU!
Applications (for example ProAgent) that require block-related
alarms (Alarm_S: SFC17-19) are not supported in multiplex mode.
Disabled (default setting)
•
All the UDP frames received by the CP are buffered until they
can be transferred to the CPU or the internal buffer overflows.
Following a buffer overflow, newly arriving frames are
discarded.
The characteristics associated with disabling the option can be
critical in certain applications with high frame traffic. Buffering
of a lot of frames may result in an undesired time offset
between the frames accumulated in the CPU and the current
frame at the Ethernet interface.
Enabled
•
The CP always transfers the last received, in other words, the
current frame to the CPU. As long as no new UDP frame can
be transferred between the CP and the CPU due to the current
communication load, only the last frame received is buffered in
the CP (memory size = 1).
Enabling achieves the shortest possible reaction time between
the arrival of the UDP frame and its evaluation on the CPU.
3.3 Setting further CP properties
49