Siemens S7-400 Installing the Central Rack CR and Expansion Rack ER, Function of the Racks

Installing the S7-400

2.2Installing the Central Rack (CR) and Expansion Rack (ER)

Function of the Racks

The racks of the S7-400 system form the basic framework which accepts the individual modules. The modules exchange data and signals and are powered via the backplane bus. The racks are designed for wall mounting, for mounting on rails, and for installation in frames and cabinets.

Racks in the S7-400 System

Rack	No. of	Available	Application	Characteristics
	Slots	Buses
UR1	18	I/O bus	CR	Rack for all module types in the S7-400.
		Communication	or
UR2	9
		bus	ER
				Racks for signal modules (SMs), receive
				IMs, and all power supply modules.
				The I/O bus has the following restric-
ER1	18			tions:
				• Interrupts from modules have no
				effect because no interrupt lines
				exist.
		Restricted I/O	ERs	• Modules are not supplied with 24 V,
		bus		i.e. modules requiring 24 V cannot
				be used (see technical data of the
				modules).
ER2	9			• Modules are neither backed up by
				the battery in the power supply
				module nor by the voltage applied
				externally to the CPU or receive IM
				(EXT.BATT. socket).
		I/O bus,		Rack for all module types in the S7-400
CR2	18	segmented	Segmented	except receive IMs.
		Communication	CR	The I/O bus is subdivided into 2 I/O bus
		bus, continuous		segments of 10 and 8 slots respectively.
CR3	4	I/O bus	CR in standard	Racks for all S7-400 module types ex-
		Communication		cept receive IMs. CPUs 41x-H only in
			systems
		bus		stand-alone operation.
		I/O bus,	Subdivided CR or	Rack for all S7-400 modules except
			ER for compact in-	send IMs.
		segmented
UR2-H	2*9		stallation of a fault--	The I/O bus and communication bus are
		Communication
			tolerant system	divided into 2 bus segments, each with 9
		bus, segmented
				slots.

2-6	Automation System S7-400	Hardware and Installation
		A5E00850741-01