Configuring Hardware and Communication Connections STEP 7.pdf

Requirements
Configuring the Distributed I/O (DP)
• The constant-bus-cycle-time master must support the "Constant bus cycle time"
function (see info text in the hardware catalog).
• The constant-bus-cycle-time master must be a class 1 DP master. This means
a PG/PC can never be a constant-bus-cycle-time master.
• The constant-bus-cycle-time master is the only active station on the
PROFIBUS-DP. Only one DP master system may be present on the
PROFIBUS subnet. Programming devices or PCs can also be connected.
• Constant bus cycle time is possible only for the "DP" and "User-Defined" bus
profiles.
• CiR must not be configured.
• No H-CPU may be connected to the PROFIBUS subnet.
• The PROFIBUS subnet must not be a cross-project one.
Time for DP Constant Bus Cycle Time
STEP 7 calculates a recommended time for the "DP constant bus cycle time(ms)"
based on:
• The PROFIBUS configuration (number of configured nodes, number of
programming devices etc.)
• Other information for the calculation which can be specified as an option (for
example, any additional not configured programming devices to be taken into
account)
You can correct this time but not below the calculated and displayed minimum
value.
Influence of Connected Active Nodes (PGs/PCs and I Slaves)
A PG/PC must only be taken into account if it is connected directly to the
PROFIBUS via its PROFIBUS interface. It does not need to be taken into account if
it is connected via the multipoint interface of the CPU, as shown in the following
figure.
If intelligent DP slaves (for example, CPU 315-2DP) are connected, the time for the
DP constant bus cycle should be calculated generously.
Configuring Hardware and Communication Connections with STEP 7
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