Siemens SIMATIC S7-400 Installation Manual page 23

Electrical Supply
The modules inserted in the rack are supplied with the required operating voltages
(5 V for logic, 24 V for interfaces) via the backplane bus and base connector, by the
power supply module fitted in the slot on the extreme left in the rack.
For local connections, ERs can also be supplied with power via the
IM 460-1 / IM 461-1 interface modules.
5 A may flow through each of the two interfaces of a send IM 460-1, meaning each
ER in a local connection can be supplied with up to 5 A.
I/O Bus
The I/O bus is a parallel backplane bus designed for the fast interchange of
I/O signals. Each rack has an I/O bus. Time-critical operations to access the
process data of the signal modules take place via the I/O bus.
Communication Bus (C Bus)
The communication bus (C bus) is a serial backplane bus designed for the fast
exchange of large volumes of data parallel to the I/O signals. Except for racks ER1
and ER2, each rack has a communication bus.
Rack with I/O Bus and Communication Bus
The following figure shows a rack with an I/O bus and a communication bus. The
I/O bus connector and communication bus connector can be seen at each slot.
When the rack is delivered, these connectors are protected by a cover.
Automation System S7-400 Hardware and Installation
A5E00850741-01
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I/O bus connector
Communication
bus connector
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Installing the S7-400
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