NORD BU0050 User Manual

SK TU1-DEV
SK TU2-DEV
SK TU3-DEV

GB

BU 0050

USS Bus modules and MODBUS RTU

Supplementary manual for NORD frequency inverters

NORD USS and Modbus RTU Manual Safety information

N O R D Frequency inverters

Safety and operating instructions for

drive power converters

(as per: Low Voltage Directive 2006/95/EEC )

1. General
During operation, drive power converters may, depending on their

protection class, have live, bare, moving or rotating parts or hot
surfaces.

Unauthorised removal of covers, improper use, incorrect installation
or operation causes a risk of serious personal injury or material
damage.

Further information can be found in this documentation.
All transportation, installation, initialisation and maintenance work

must be carried out by qualified personnel (compliant with
IEC 364, CENELEC HD 384, DIN VDE 0100, IEC 664 or
DIN VDE 0110, and national accident prevention regulations).

For the purposes of these basic safety instructions, qualified
personnel are persons who are familiar with the assembly,
installation, commissioning and operation of this product and who
have the relevant qualifications for their work.

2. Proper use in Europe

Drive power converters are components intended for installation in
electrical systems or machines.

When installed in machines, the drive power converter cannot be
commissioned (i.e. commencement of the proper use) until it has
been ensured that the machine meets the provisions of the EC
Directive 2006/42/EEC (Machine Directive); EN 60204 must also be
complied with.

Commissioning (i.e. implementation of the proper use) is only
permitted if the EMC Directive (2004/108/EEC) is complied with.

Drive power converters with the CE mark meet the requirements of
the Low Voltage Directive 2006/95/EEC. The harmonized standards
stated in the Declaration of Conformity are used for the drive power
converters.

Technical data and information for connection conditions can be
found on the name plate and in the documentation, and must be
complied with.

The drive power converters may only be used for the safety
functions which are described and for which they have been
explicitly approved.

3. Transport, storage

Information regarding transport, storage and correct handling must
be complied with.

4. Installation

The installation and cooling of the equipment must be implemented
according to the regulations in the corresponding documentation.

The drive power converters must be protected against
impermissible loads. Especially during transport and
handling, components must not be deformed and/or
insulation distances must not be changed. Touching of
electronic components and contacts must be avoided.

Drive power converters have electrostatically sensitive
components, which can be easily damaged by incorrect
handling. Electrical components must not be mechanically
damaged or destroyed (this may cause a health hazard!).

5. Electrical connections

When working on live drive power converters, the applicable
national accident prevention regulations must be complied
with (e.g. VBG A3, formerly VBG 4).

The electrical installation must be implemented according to
the applicable regulations (e.g. cable cross-section, fuses,
ground lead connections). Further information is contained
in the documentation.

Information about EMC-compliant installation – such as
shielding, earthing, location of filters and installation of
cables can be found in the drive power converter
documentation. These instructions must be complied with
even with CE marked drive power converters. Compliance
with the limiting values specified in the EMC regulations is
the responsibility of the manufacturer of the system or
machine.

6. Operation

Where necessary, systems where drive power converters
are installed must be equipped with additional monitoring
and protective equipment according to the applicable safety
requirements, e.g. legislation concerning technical
equipment, accident prevention regulations, etc.

The parameterisation and configuration of the drive power
converter must be selected so that no hazards can occur.

All covers must be kept closed during operation.

7. Maintenance and repairs

After the drive power converter is disconnected from the
power supply, live equipment components and power
connections should not be touched immediately, because of
possible charged capacitors. Observe the relevant
information signs located on the drive power converter.

Further information can be found in this documentation.

These safety instructions must be kept in a safe place!

2 Subject to technical amendments BU 0050 GB-3111

NORD USS and Modbus RTU Manual Concerning this document

Designation of
previous issues

Software
Version

Comments

BU 0500 GB, December 2004
Part No. 607 0502 / 5204

Latest version

BU 0050 GB, August 2011
Part No. 607 0502 / 3111

 Deletion of option "DevicenNet mc" for FI series

"vector mc"

 Inclusion of SK 500E series frequency inverters
 Implementation of Modbus RTU (for SK 500E)

NOTE

This supplementary operating manual is only valid in conjunction with the operating manual
supplied for the respective frequency inverter.

Documentation

Designation: BU 0050 GB
Part No.: 607 05 01
Device series: USS for SK 300E, SK 500E (entire series), SK 700E, SK 750E
Modbus RTU for SK 540E and SK 545E

Version list

Publisher

Getriebebau NORD GmbH & Co. KG

Rudolf-Diesel-Str. 1  D-22941 Bargteheide  http://www.nord.com/
Tel.: [phone] / 401-0  Fax [phone] / 401-555

BU 0050 GB-3111 Subject to technical amendments 3

NORD DeviceNet Manual Concerning this document

Intended use of the frequency inverter

Compliance with the operating instructions is necessary for fault-free operation and the

acceptance of any warranty claims. These operating instructions must be read before
working with the device!

These operating instructions contain important information about servicing. They must
therefore be kept close to the device.

The described optional modules can only be used for the specifically defined frequency
inverter series, use across series is only possible with the SK TU2-… module with SK 300E
and SK 750E. The use of these modules with other devices is not permitted and can lead to
their destruction.

The described optional modules and the corresponding frequency inverters are devices for
stationary installation in control cabinets or decentralised structures. All details
regarding technical data and permissible conditions at the installation site must be
complied with.

Commissioning (commencement of the intended use) is not permitted until it has been ensured
that the machine complies with the EMC Directive 204/108/EEC and that the conformity of
the end product meets the Machinery Directive 2006/42/EEC (observe EN 60204).

 Getriebebau NORD GmbH & Co. KG, 2011

4 Subject to technical amendments BU 0050 GB-3111

Contents

FOREWORD ................................................................................................................................ 7

1 USS ........................................................................................................................................... 7

1.1 General information .............................................................................................. 7

1.1.1 The USS Protocol ..................................................................................................... 7

1.1.2 Features .................................................................................................................... 7

1.1.3 Delivery ..................................................................................................................... 7

1.1.4 Scope of supply ......................................................................................................... 8

1.1.5 Certifications ............................................................................................................. 8

1.1.6 Identification System ................................................................................................. 8

1.2 Modules ................................................................................................................ 9

1.2.1 SK 500E .................................................................................................................... 9

1.2.2 SK 700E .................................................................................................................. 12

1.2.3 SK 300E .................................................................................................................. 18

1.3 USS Protocol Specification ................................................................................ 19

1.3.1 General information................................................................................................. 19

1.3.2 Telegram Structure ................................................................................................. 19

1.3.3 Data Coding ............................................................................................................ 20

1.3.4 Character Frame ..................................................................................................... 20

1.3.5 Transfer Procedure ................................................................................................. 21

1.3.6 Start Pause Time .................................................................................................... 21

1.3.7 Response Delay Time ............................................................................................. 22

1.4 Bus Configuration ............................................................................................... 23

1.4.1 General information................................................................................................. 23

1.4.2 Topology ................................................................................................................. 23

1.4.3 Transfer Method ...................................................................................................... 23

1.4.4 Installation of the Bus System ................................................................................. 24

1.5 Data transmission ............................................................................................... 26

1.5.1 Structure of reference data ..................................................................................... 26

1.5.2 PPO types ................................................................................................ ............... 27

1.5.3 Process data (PZD)................................................................................................. 29

1.5.4 Parameter range (PKW) .......................................................................................... 39

1.6 Telegram examples ............................................................................................ 43

1.6.1 The Macro Generator .............................................................................................. 43

1.6.2 Switch-on block  Standby .................................................................................... 44

1.6.3 Enable with 50% setpoint ........................................................................................ 46

1.6.4 Writing a parameter................................................................................................. 47

1.6.5 Reading the acceleration time parameter ............................................................... 48

1.7 Master Telegram Times ..................................................................................... 49

1.8 Frequency Inverter Settings ............................................................................... 50

1.8.1 Frequency inverter bus parameters ........................................................................ 50

2 MODBUS RTU ........................................................................................................................ 61

2.1 The bus system .................................................................................................. 61

2.2 Features ............................................................................................................. 61

2.3 Telegram Structure ............................................................................................. 62

2.4 RTU Frames ....................................................................................................... 62

2.5 Function Codes .................................................................................................. 62

2.5.1 01h Read Coil ......................................................................................................... 63

2.5.2 05h Write Single Coils ............................................................................................. 63

2.5.3 0Fh Write Multiple Coils .......................................................................................... 64

2.5.4 03h Read Holding Register ..................................................................................... 65

2.5.5 06h Write Single Register ....................................................................................... 66

2.5.6 10h Write Multiple Register ..................................................................................... 66

2.6 Exception Responses ......................................................................................... 68

2.7 Watchdog ........................................................................................................... 68

2.8 Description of parameters .................................................................................. 69

BU 0050 GB-3111 Subject to technical amendments 5

NORD USS and Modbus RTU Manual

3 FAULTS .................................................................................................................................. 71

3.1 Troubleshooting ................................................................................................. 71

3.1.1 Error display............................................................................................................ 71

3.1.2 Error memory .......................................................................................................... 71

3.2 Error messages ................................................................................................. 72

4 ADDITIONAL INFORMATION ............................................................................................... 73

4.1 Maintenance and servicing information ............................................................. 73

4.2 Abbreviations in this manual .............................................................................. 73

5 KEYWORD INDEX ................................................................................................................. 74

6 Subject to technical amendments BU 0050 GB-3111

1.1 USS - General information

Foreword

This supplementary documentation is valid for the SK 300E, SK 500E, SK 700E series and for the SK 750E.
It describes the setup of communication via RS485.

For this, the main emphasis is on communication according to the USS protocol. Corresponding optional
modules are available for the SK 700E and SK 750E series. The SK 300E and SK 500E series have an
appropriate interface integrated as standard.

In addition, the requirements of Modbus communication (SK 540E and higher) will be considered.

1 USS

1.1 General information

1.1.1 The USS Protocol

With the aid of the USS protocol, a user can set up a serial bus coupling between a higher level Master and
several slave systems. Master systems can for example be memory programmable control units (SPS) or
PCs.

The USS protocol allows the user to implement automation tasks with conveying according to time-cycled
telegram traffic (fixed telegram length required), as well as visualisation tasks.

The USS protocol is a simple, serial transfer protocol defined by Siemens, which if fully tailored to the needs
of drive technology.

1.1.2 Features

Support of a multiple point coupling, e.g. EIA RS 485 hardware or a point-to-point coupling, e.g. EIA RS 232.

 Master / Slave access procedure
 Single Master System
 Maximum 32 participants (maximum 31 slaves)
 Simple, secure telegram framework
 Same physical bus design as PROFIBUS (DIN 19245 Part 1)
 The data interface to the basic device is according to the PROFILE for variable speed drives.

This means that with USS, the information to the drive unit is transferred in the same way as with the
PROFIBUS-DP.

 Can be used for commissioning, service and automation
 Service tools on PC (NORD CON)
 Simple to implement in customer-specific systems-

1.1.3 Delivery

Check the equipment immediately after delivery/unpacking for transport damage such as deformation or
loose parts.

If there is any damage, contact the carrier immediately and carry out a thorough assessment.

Important! This also applies even if the packaging is undamaged.

BU 0050 GB-3111 Subject to technical amendments 7

NORD USS and Modbus RTU Manual

SK TU1-RS2

Bus system: AS1 = AS-Interface, CAN = CAN, CAO = CANopen,
RS2 = RS232, USS = USS, etc.
Device series: SK TU1 / SK TU2 / SK TU3

1.1.4 Scope of supply

SK TU1-RS232* for frequency inverter SK 700E IP20 or
SK CU1-STD for frequency inverter SK 700E, SK 750E IP20 or
SK CU1-USS for frequency inverter SK 700E, SK 750E IP20 or

*incl. screw for optional fixing to the FI

1.1.5 Certifications

1.1.5.1 European EMC Directive

If NORD frequency inverters or their options are installed according to the
recommendations in this instruction manual, it meets all EMC directive
requirements, as per the EMC product standard for motor-operated systems
EN 61800-3.

1.1.5.2 RoHS compliance

The bus options described here are designed to be RoHS compliant
according to Directive 2002/95/EEC

1.1.6 Identification System

8 Subject to technical amendments BU 0050 GB-3111

1.2 USS - Modules

WARNING

NOTE

Modules should not be inserted or removed unless the device is free of voltage. The slots may
only be used for the intended modules.

Installation of a technology unit separate from the frequency inverter is not possible. It must be
connected directly to the frequency inverter.

LED

red/green

1.2 Modules

1.2.1 SK 500E

1.2.1.1 General

By the use of various modules for display, control and parameterisation, the SK 5xxE can be easily adapted
to various requirements.

Alphanumerical display and operating modules can be used for simple commissioning. For more complex
tasks, various connections to a PC or an automation system can be selected.

The technology unit (Technology Unit, SK TU3-…) is connected externally to the frequency inverter and is
therefore easy to access and replace at any time.

As delivered, without the technology unit, 2 LEDs (green/red) are visible externally. These indicate the actual
device status.

The green LED indicates that the mains voltage is present and operational, while a flashing code that
increases in speed shows the degree of overload at the frequency inverter output.

The red LED signals actual error by flashing with a frequency which corresponds to the number code of the
error (Manual BU 0500 Section 6).

BU 0050 GB-3111 Subject to technical amendments 9

NORD USS and Modbus RTU Manual

X7: additional terminal

block with RS485
interface
(terminals 73/74)

SK 520Eor higher

X11: 1x RJ12 socket to

connect the RS232
or RS485 interface

X11

1.2.1.2 RS 485 interface

As standard, all devices in the SK 500E series have an integrated interface for USS bus communication.
According the version of the Fi, the following interfces are available:
X11 RJ12 socket (available for the entire series)
X7:73/74 RS485 + / - terminal connection (available for SK 520E or higher)

10 Subject to technical amendments BU 0050 GB-3111

1.2 USS - Modules

Contact

Function

Data

Description / wiring suggestion

DIP switch 1/2 (top side of frequency inverter)

DIP-1

Termination resistor for RS485 interface
(RJ12); ON = switched in
[Default = "OFF"]
For RS232 communication DIP1 to "OFF"

X11 X10 X9

RS4 85 _ A

RS4 85 _B

G N D

TXD

RXD

+ 5V

1 2

ON

CAN _H

CAN _L

CAN _GN DncCAN _SHLD

CAN _GN DncCAN _24 V

CAN _H

CAN _L

CAN _GN DncCAN _SHLD

CAN _GN DncCAN _24 V

RS48 5_A

RS48 5_B

GN D

TXD

RXD

+ 5 V

SK 511E and above

RS232/485 DIP CAN/CANopen

DIP-2
Termination resistor for CAN/CANopen

interface (RJ12); ON = switched in
[Default = "OFF"]

Terminal

Function

Data

Description / wiring suggestion

X7:73

Data cable RS485

Baud rate
9600…38400Baud

Termination resistor
R=120

BUS connection parallel to RS485 on RJ12 plug
NOTE: The termination resistance of DIP switch 1 (see

RJ12/RJ45) can also be used for contacts 73/74.

X7:74

NOTE

To ensure reliable communication, a termination resistor (DIP switch DIP1) must be set at both
ends of the bus.

RJ 12 socket (X11)
In addition to the RS485 interface, the RJ12 socket also provides an interface for communication via RS 232.

However, the RS232 interface is only intended for connecting a PC.
If a network is to be set up with several participants which communicate via USS (frequency inverters), it

must be noted that communication must be via RS 485.
The RS232 interface (contacts X11:TXD and X11:RXD) cannot be deactivated on the frequency inverter. In

order to prevent a short circuit of these data cables and therefore the destruction of the RS232 driver, the
contacts TXD, RXD and +5V must not have a common connection to several frequency inverters.

Terminal connection (X7:73/74)
Above configuration level SK520E the frequency inverters are equipped with an additional terminal block

(X7). This provides the possibility of setting up the RS485 bus communication via contacts 73 and 74.

BU 0050 GB-3111 Subject to technical amendments 11

NORD USS and Modbus RTU Manual

Technology units (Technology Units) are modules which can be inserted
from above for display, parameterisation and control of the inverter.

WARNING

NOTE

Modules must not be inserted or removed unless the device is free of voltage. The slots may

only be used for the intended modules. The slots are coded to prevent them from being
incorrectly connected.

Installation of a technology unit separate from the frequency inverter is not possible. It must be

connected directly to the frequency inverter.

Customer interfaces (Customer Units) are modules which are
inserted into the upper slot inside the inverter. They are used for
control and communication using digital/analog signals or bus
interfaces.

Special extensions (EXtension Units) are inserted into the lower slot of
the inverter. Such an extension unit is required if the speed is to be
controlled or positioning is to be carried out by an incremental (absolute)
encoder.

1.2.2 SK 700E

1.2.2.1 General

With the combination of modules for display, technology units and modules with digital and analog inputs
and interfaces, customer interfaces or special extensions, the SK 700E can be easily extended to cater
for the requirements of a wide range of applications.

12 Subject to technical amendments BU 0050 GB-3111

WARNING

NOTE

Modules must not be inserted or removed unless the device is free of voltage. The slots may
only be used for the intended modules.

Installation of a technology unit separate from the frequency inverter is not possible. It must be
connected directly to the frequency inverter.

RXD

0V

TXD

6 1 5

9

5V

700E

N O RD A C

700E

N O RD A C

1.2.2.2 Technology Box RS232

(SK TU1-RS2, Option)

The Technology Box (Technology Unit) is clipped to the outside of the inverter.
The RS232 interface enables simple connection of an SK 700E to a PC with a

serial interface.
Communication between PC and frequency inverter can be set up using the

NORD CON Software (Windows). This is used for the control, parameterisation
and display of operating values of the frequency inverter.

This allows a simple functional test of the inverter to be carried out and,
following successful parameterisation, the data set can be saved as a file.

1.2.2.3 Installation of the SK TU1 technology unit

1.2 USS - Modules

Installation of the technology units must be carried out as follows:

1. Switch off the mains voltage, observe the waiting period.

2. Remove the dummy cover by actuating the unlocking device on the top and bottom edge.

3. Allow the technology unit to engage audibly by pressing lightly on the mounting surface.

BU 0050 GB-3111 Subject to technical amendments 13

NORD USS and Modbus RTU Manual

Connector

Functions

Maximum cross-section

Parameter

X1.1

Output relay

1,5 mm2

P434 ... P443

X1.2

Analog signals IN / OUT

1,0 mm2

P400 ... P419

X1.3

Digital inputs

1,0 mm2

P420 ... P423

X1.4

Bus signals / power supply

1,0 mm2

P503 ... P548

74 RS485 -

X1.1

X1.2

X1.3

X1.4

11 VREF 10V
12 AGND /0V
13 AIN1 ­14 AIN1 +
17 AOUT1

21 DIG IN 1
22 DIG IN 2
23 DIG IN 3
24 DIG IN 4
42 VO +15V

41 VO +5V
40 GND /0V
73 RS485 +

01 REL1.1
02 REL1.2
03 REL2.1
04 REL2.2

NOTE: All control voltages are based on a common reference potential!

Potentials AGND /0V and GND /0V are internally linked in the device.

The maximum total current 5/15V is 300mA!

Potentialfreier Kontakt oder
Ausgang einer SPS: 7,5...33V

(low = 0...3,5Volt)

Differenzeingang 0...10V

0...20mA

Voltage supply: 5V
RS 485 (USS protocol)

5V supply for ParameterBox,
p-box or motor thermistor

Data cables USS protocol

Digitale Eingänge:
DIG IN 1 = Ein rechts
DIG IN 2 = Ein links
DIG IN 3 = Parametersatz bit 0
DIG IN 4 = Festfrequenz 1

Ausgangsrelais:
max. 2,0A
28V DC /230V AC

U

REF

= 10V / I

max

= 10 mA

Analogausgang SPS: 0...10V
oder Potentiometer: 2...10k

Spannungsversorgung: 15V

Termination resistor for
RS 485 interface (120)

Zuschaltbarer Bürdenwiderstand für
0/4...20mA Analogeingang (250)

U/I switching

Analog input,

250

ON = Current,

OFF = Voltage

Termination

resistor

RS 485

120

O
F
F

O
F
F

1.2.2.4 Customer unit Standard I/O

(SK CU1-STD, Option)

The standard I/O of the customer interface(Customer Unit) provides
sufficient control terminals for most applications and it is fully
terminal-compatible with NORDAC vector mc..

1 analog differential input, 4 digital inputs and 1 analog output are
available for control of the frequency inverter.

Readiness for operation is shown via the 2 relay contacts and a
mechanical motor brake is activated at the correct time.

The connected frequency inverter can be accessed via the RS485
interface. In addition to the entire range of control functions,
parameterisation is also possible.

TheNORD CON software can be used to carry out a simple function
test of the serial interface and the parameterisation of the inverter.
For this, an interface converter (e.g. SK IC1-232/485) must be used
between the PC and the inverter. Following successful
parameterisation, the complete data set can be stored as a file by
means of NORD CON.

14 Subject to technical amendments BU 0050 GB-3111

1.2 USS - Modules

Connector

Functions

Maximum cross-section

Parameter

X4.1

Output relay

1,5 mm2

P434 ... P436

X4.2

Digital input

1,5 mm2

P420

X4.3

Data cables

1,5 mm2

P503 ... P548

NOTE: All control voltages are based on a common reference potential!

Potentials AGND /0V and GND /0V are internally linked in the device.

The maximum total current 5/15V is 300mA!

X4.1

X4.2

X4.3

01 REL1.1
02 REL1.2

41 VO +5V
40 GND /0V
73 RS485+
74 RS485-

21 DIG IN 1

42 VO +15V

Data cables:
RS485

(terminal 73-74, RS485 +/-)

Control signal: 2.5 ... 33V

Output relay:
Max. 2.0A
28V DC /230 V AC

Digital input 1 (P420)

Voltage supply: 15V

USS

USS termination resistor

not connected

connected

ON

1.2.2.5 USS Customer Interface

(SK CU1-USS, Option)

In addition to data connections, the USS customer units are also
equipped with conventional digital inputs and outputs.

Via the existing relay contacts, a mechanical motor brake can be
controlled or readiness for operation can be communicated to a
higher level system.

The digital input has a 2.5V switching threshold for the evaluation
of the temperature sensor. The input can, however, also be used
for an emergency stop function.

BU 0050 GB-3111 Subject to technical amendments 15

NORD USS and Modbus RTU Manual

WARNING

NOTE

Installation must be carried out by qualified personnel only, paying particular
attention to safety and warning instructions.

A customer interface must not be replaced while it is carrying voltage.

Kundenschnittstelle

Sondererweiterung

Technologiebox

Verrieglungsstift

CLOSED

OPEN

Verriegelung geschlossen
Verriegelung geöffnet

Locking pin

Technology unit

Customer interface

Special extension
unit

Locking device closed

Locking device open

1.2.2.6 Installation of customer units

1. Switch off the mains voltage, observe
the waiting period.

2. Remove the cover grid from the
connection area by loosening the 2
screws and levering out the device cover
(slot) or simply pull it out.

3. Locking lever in the "open" position.

4. Using light pressure push the customer
unit into the upper guide rail until it
engages.

5. Move the locking lever to the "closed"
position.

6. Remove the connector by pressing the
releases then make the necessary
connections. Then insert the connectors
until they engage.

7. Replace all covers.

16 Subject to technical amendments BU 0050 GB-3111

1.2 USS - Modules

Motor
PTC

Supply voltage
+5V

Digital
input

Removing customer units:

1. Switch off the mains voltage, observe the waiting period.

2. Remove the cover grid from the connection area by loosening the 2 screws and levering out the device
cover (slot) or simply pull it out.

3. Locking lever in the "open" position.

4. Using a screwdriver (as shown), lever the customer unit out of its engaged position and then remove it by
hand.

5. Move the locking lever to the "closed" position.

6. Replace all covers.

Motor temperature protection applies for all customer units!

For secure protection against motor overheating, a
temperature sensor (thermistor, PTC) can be connected
to any digital input.

The appropriate parameters (P420 ... P425, depending on
option) must be set to a value of 13 (PTC thermistor input)
for this purpose.

The supply voltage varies dependent upon the customer
unit. The lowest voltage possible should be chosen.

Internal switching in the inverter prevents excessive PTC
voltage.

The cable routing should always be separate from the motor cable and with shielded cables.

BU 0050 GB-3111 Subject to technical amendments 17

NORD USS and Modbus RTU Manual

M12 connector (Detail 1)

Terminal (Detail 2)

Functions

Maximum cross-section

4 (black)

73

RS485 +

1,5 mm2

3 (blue)

74

RS485 -

1,5 mm2

2 (white)

41

+5V

1,5 mm

2

1 (brown)

40

0V, GND

1,5 mm2

3,0 m

1

2

1.2.3 SK 300E

Technology units and customer interfaces

Through the combination of modules for the
display, (technology units) and modules with
digital and analog inputs, as well as interfaces,
(customer units) or bus interfaces, the SK 300E
can be easily adapted to the requirements of a
wide range of applications.

The NORD CON software can be used to carry
out a simple function test of the serial interface
and parameterisation of the inverter. For this, an
interface converter (e.g. SK IC1-232/485) must
be used between the PC and the inverter.
Following successful parameterisation, the
complete data set can be stored as a file by
means of NORD CON.

Further details can be found in Manual BU 0300.

USS interface (RS485)

With the SK 300E, an RS485 interface is lead out to a 4-pin M12
round connector (Detail 1) as standard. In addition to being used
for external control (ParameterBox) it can also be used as a bus
interface.

If required an M12  SUB D9 (Part No.. 278910060) connecting
cable is available.

Parallel to the external M12 connection, in the connection unit
(trio interface, removed from FI) terminals 73/74 are also
available for connection.

The RS485 termination resistor (Detail 2) can be switched in or
out using the DIP switch in the connection unit.

18 Subject to technical amendments BU 0050 GB-3111

1.3 USS - Protocol speciication

STX

LGE

ADR

N1

N2

..

Nn

BCC

1.3 USS Protocol Specification

1.3.1 General information

The USS protocol defines an access procedure according to the Master/Slave principle for communication
via a serial bus. A sub-set of this also includes point-to-point connection. A master and a maximum of 31
slaves can be connected to a bus. The individual slaves are accessed by the master via an address
character in the telegram. Direct exchange of messages between the individual slaves is not possible.
Communication is carried out in semi-duplex mode. The master function cannot be transferred (single master
system).

Data transfer via the two-cable bus is carried out by individual characters in the format:
1 start bit, 8 data bits 1 even parity bit and 1 stop bit (8E1) - This results in a character frame of 11 bits.

The direction of the data on the bus (transmit or receive) is specified by the master.

1.3.2 Telegram Structure

Each telegram starts with the start character STX (= 02 Hex), followed by the length (LGE) and the address
byte (ADR). This is followed by the information characters. The telegram

is concluded by the data saving character BCC (Block Check Character).

For word information (16 Bit) in the information data block (= information character block) the High Byte (first
character) is always transmitted first, followed by the Low Byte (second character). The same applies for
double-word information:

First the High Word is transmitted, followed by the Low Word.

BU 0050 GB-3111 Subject to technical amendments 19

NORD USS and Modbus RTU Manual

STX

(Start of Text): ASCII character: 02 Hex
The start character forms the first character in the telegram and together with the start pause it is used

for reliable detection of the start of the telegram.

LGE

(Telegram length): 1 Byte, contains the length of the telegram.
The telegram length is located in the 2nd byte of the telegram and indicates the length of the telegram

from the 3rd byte onwards. Specification of the length enables differentiation between the various types
of telegram. The data recipient can use the length byte to check the number of characters to be
received.

ADR

(Address byte): 1 byte, also contains the slave address.

Bit7 Bit6 Bit5 Bit4 Bit3 Bit2 Bit1 Bit0

0 M BC | Address (0..30) |

The USS address is located in the 3rd byte (data bits 0 to 4) of the telegram. The slave device which is
to transmit or receive data is identified via the USS address. Therefore, a maximum of one slave device
can be represented by each of the 31 possible addresses For this, the appropriate address must be set
in the slave device. Bit 5 and Bit 6 have a special meaning.

Bit 5 Broadcast: A so-called broadcast telegram can be triggered by setting this bit. In a broadcast
telegram, address bits 0 to 4 are ignored by the connected slaves, i.e. the transmitted telegram is
processed by all of the slaves. However, in contrast to standard addressing, the slaves do not transmit a
response telegram as this would result in bus conflicts.

Bit 6 Echo: By setting the 6th bit, the inverter returns a telegram which is identical to the one which it
has received (for commissioning).

N1... Nn

Information characters: each one byte, content depending on task

BCC

1 byte, data saving character (Block Check Character)
The check-sum BCC is formed byte-wise over the entire telegram as an Exclusive OR link. The result

after the last net character is then the BCC.

BCC = STX XOR LGE XOR ADR XOR N1 XOR....N

N

1.3.3 Data Coding

1.3.4 Character Frame

Each transmitted character begins with a start bit (logical 0) and end with a stop bit (logical 1). 8 bits (1 byte)
are transmitted. Saving is performed by a parity bit (even parity). Therefore 11 bits are transmitted for each
character.

20 Subject to technical amendments BU 0050 GB-3111

1.3 USS - Protocol speciication

Time

Size

Meaning

t

SP

Minimum 2 character durations*

Start pause time

t

AVZ

Maximum 20 ms

Response Delay Time

t

TLZ

1.5 x consecutive telegram duration

= 1,5 x (n+4) x character duration

Max. residual telegram duration

t

ZVZ

Smallest start pause time

Character delay time

*Character duration = 11 x (1/Baud rate)

Master

BCC

LGE

ADR

1. n BCC

STX

STX

LGE

ADR

1. n BCC

t

SP

t

AVZ

STX

t

SP

t

TLZ

Slave

x

x+1

t

ZVZ

1.3.5 Transfer Procedure

The USS protocol functions according to the master/slave principle, whereby the master is the control device
(PC, SPS etc) and the slaves are the frequency inverters

Only one slave can be addressed with each telegram (exception: broadcast telegram without response by
the slaves).

In order to ensure reliable detection of the start of the telegram by the slave, the master must observe a so­called start pause between the receipt of the slave telegram and transmission of the next telegram. The
master starts to transmit a telegram. After the data package has been sent, the master switches the bus data
direction from transmission to reception. The slave addressed in the telegram must respond within a
specified response time.

The lengths of the master and slave telegrams are the same, i.e. the master telegram determines the length
of the response by the slave.

Telegram traffic can be cyclical a acyclical.

The following time definitions must be observed:

1.3.6 Start Pause Time

The start character STX (= 02 Hex) on its own is not sufficient to enable the slaves to uniquely identify the
start of a telegram, because the bit combination 02/Hex may also occur in the information characters.
Therefore, in advance of the STX a start pause time tSP where no characters are sent for at least the
duration of 2 characters is specified for the master. The start pause time is a component of the order
telegram. A valid telegram is only identified by an STX with a preceding start pause.

The exchange of data is always performed according to the pattern described above (semi-duplex
operation):

The minimum start pause time which is to be observed for the various baud rates can be found in the Master
Telegram Time table in the Additional Information section.

BU 0050 GB-3111 Subject to technical amendments 21

NORD USS and Modbus RTU Manual

1.3.7 Response Delay Time

The time interval between the last character of the order telegram (BCC) and the start of the response
telegram (STX) is called the response delay time t
20ms, however, it must not be smaller than the start pause. If the addressed participant does not
respond within the maximum permissible response delay time, an error message is saved in the master. The
master then sends the telegram which is intended for the next slave.

The minimum response delay time which is to be observed for the various baud rates can be found in the
Master Telegram Time table in the Additional Information section.

. The maximum permissible response delay time is

AVZ

22 Subject to technical amendments BU 0050 GB-3111

1.4 USS - Bus structure

1.4 Bus Configuration

1.4.1 General information

The basis for the physical interface of the USS protocol is the 'Recommended Standard RS-485'
For point-to-point connections, a sub-set of EIA RS-232 (CCITT V.24), TTY (20mA current loop) or optic fibre

cable can be used as the physical interface.
SK 300E and SK 500E series inverters are always configured with an RS485 interface on the terminal

connection bar or connector. For SK 700E series devices, the customer interface standard or USS must be
selected.

For the SK 700E series, RS 232 technology modules can be used for communication (only point-to-point
communication possible)

1.4.2 Topology

The USS bus is based on a linear topology without spur cables. Both ends of the lines end at a participant and
must be terminated there with bus termination networks.

The maximum cable length and the maximum distance between the master and the last slave is restricted by
the properties of the cable, the ambient conditions and the transfer rate. With a transfer rate < 100kbit/s, a
maximum length of 1200m is possible.

[EIA Standard RS-422-A December 1978, Appendix, Page 14]
The number of participants is restricted to 32 (1 master, 31 slaves).

1.4.3 Transfer Method

Transfer is by the half-duplex method, i.e. alternation between transmission and reception, and must be
controlled by the software. The half-duplex method allows the use of the same cables for both transfer
directions.

This enables simple and low-cost bus wiring, operation in environments where there is interference as well as
a high data transfer rate.

BU 0050 GB-3111 Subject to technical amendments 23