WEG SSW900-CRS485-W User manual

Motors | Automation | Energy | Transmission & Distribution | Coatings
Modbus RTU
SSW900-CRS485-W
User’s Guide

Modbus RTU User’s Guide
Series: SSW900
Software version: 1.5X
Language: English
Document: 10004628707 / 05
Build 6066
Publication Date: 09/2022

Summary of Revisions
The information below describes the reviews made in this manual.
Version Revision Description
V1.0X R00 First edition
V1.1X R01 General revision
V1.2X R02 General revision
V1.3X R03 Parameters related to the SSW900-CETH-W accessory. Parameter for adjusting the contrast of
the HMI display. Text corrections.
V1.4X R04 C6.2.1, C11.4. Text corrections.
V1.5X R05 General revision

Contents
Contents
ABOUT THE MANUAL .............................................. ..................................... 6
ABBREVIATIONS AND DEFINITIONS ........................................................................ 6
NUMERICAL REPRESENTATION ............................................................................. 6
DOCUMENTS .................................................................................................... 6
1 MAIN CHARACTERISTICS ........................................................................ 7
2 MODBUS COMMUNICATION INTRODUCTION ........................................ 8
2.1 MESSAGE STRUCTURE ................................................................................. 8
2.2 MODBUS RTU ......................................................................... .................... 9
3 INTERFACE DESCRIPTION.......................................................................10
3.1 RS485 ACCESSORY ...................................................................................... 10
3.2 CONNECTOR .............................................................................................. 10
3.3 TERMINATING RESISTOR ......................................................................... ...... 11
3.4 INDICATION LEDS ........................................................................................ 11
4 INSTALLATION OF THE EQUIPMENT IN NETWORK ..............................12
4.1 COMMUNICATION RATE ................................................................................. 12
4.2 ADDRESS IN THE MODBUS RTU NETWORK ......................................................... 12
4.3 TERMINATION RESISTOR ......................................................................... ...... 12
4.4 CABLES .................................................................................................... 12
4.5 CONNECTION IN THE NETWORK ...................................................................... 12
4.6 RECOMMENDATIONS FOR GROUNDING AND CABLE PASSAGE ................................ 13
5 S STATUS ...................................................................................................14
S5 COMMUNICATIONS ......................................................................................... 14
S5.1 Status Word.......................................................................................... 14
S5.2 Command Word ..................................................................................... 14
S5.3 Value for Outputs ................................................................................... 15
S5.3.2 Value for AO ............................................................................... 15
S5.4 RS485 Serial ......................................................................................... 16
6 C CONFIGURATIONS.................................................................................17
C8 COMMUNICATIONS ......................................................................................... 17
C8.1 I/O Data ............................................................................................... 17
C8.1.1 Data Read.................................................................................. 17
C8.1.2 Data Write.................................................................................. 18
C8.2 RS485 Serial .......... ............................................................................... 20
C8.2.5 Timeout ..................................... ............................................... 21
7 OPERATION IN THE MODBUS RTU NETWORK – SLAVE MODE ..........23
7.1 AVAILABLE FUNCTIONS ................................................................................. 23
7.2 MEMORY MAP ............................................................................................. 23
7.2.1 Parameters ........................................................................................ 23
7.2.2 Memory Markers .................................................................................. 24
7.2.3 Indirect Parameters .............................................................................. 24
7.2.4 Input words ........................... ............................................................ 24
7.2.5 Output Words .................................................................................... 26
7.3 DATA ACCESS............................................................................................. 27

Contents
7.4 COMMUNICATION ERRORS ............................................................................. 27
8 STARTUP GUIDE........................................................................................28
8.1 INSTALLING THE ACCESSORY ......................................................................... 28
8.2 CONFIGURING THE EQUIPMENT....................................................................... 28
8.3 CONFIGURING THE MASTER ........................................................................... 28
8.4 COMMUNICATION STATUS .............................................................................. 28
9 FAULTS AND ALARMS..............................................................................30
10QUICK REFERENCES ...............................................................................31
10.1 PARAMETER STRUCTURE .............................................................................. 31
10.2 PARAMETERS ............................................................................................. 33

ABOUT THE MANUAL
ABOUT THE MANUAL
This manual supplies the necessary information for the operation of the SSW900 soft-starter using the Modbus
RTU protocol. This manual must be used together with the SSW900 user’s manual and programming manual.
ABBREVIATIONS AND DEFINITIONS
ASCII American Standard Code for Information Interchange
CRC Cycling Redundancy Check
EIA Electronic Industries Alliance
RTU Remote Terminal Unit
TIA Telecommunications Industry Association
LSB Least Significant Bit/Byte
MSB Most Significant Bit/Byte
ro Read only
rw Read/write
cfg Configuration
NUMERICAL REPRESENTATION
Decimal numbers are represented by means of digits without suffix. Hexadecimal numbers are represented
with the letter ‘h’ after the number. Binary numbers are represented with the letter ‘b’ after the number.
DOCUMENTS
The Modbus protocol was developed based on the following specifications and documents:
Document Version Source
MODBUS Application Protocol Specification, December 28th 2006. V1.1b MODBUS.ORG
MODBUS Protocol Reference Guide, June 1996. Rev. J MODICON
MODBUS over Serial Line, December 20th 2006. V1.02 MODBUS.ORG
In order to obtain this documentation, consult MODBUS.ORG, which is nowadays the organization that keeps,
publishes and updates the information related to the Modbus protocol.
SSW900 | 6

MAIN CHARACTERISTICS
1 MAIN CHARACTERISTICS
Below are the main characteristics for Modbus RTU communication of the soft-starter SSW900.
•Interface galvanically insulated and with differential signal, providing more robustness against electromagnetic
interference.
•It allows the device to operate as Modbus RTU slave.
•Allows data communication for equipment operation and parameterization.
SSW900 | 7

MODBUS COMMUNICATION INTRODUCTION
2 MODBUS COMMUNICATION INTRODUCTION
The Modbus protocol was initially developed in 1979 by Modicon. Nowadays, it is a widely spread open protocol,
used by several manufactures in many equipments. It is a protocol of application layer for communication
between devices, especially used by industrial automation systems.
2.1 MESSAGE STRUCTURE
Modbus is a protocol based on transactions, which consist of a request followed by a response. Every com-
munication begins with the client (master) making a request to a server (slave), which answers what has been
asked.
The communication is based on a packet called PDU (Protocol Data Unit) which is defined by the specification
of the protocol in three types:
•Request PDU:
Function Code: specifies the kind of service or function requested.
Function Data: specific function data.
•Response PDU:
Function Code: code of the function corresponding to the request.
Response Data: specific function data.
•Exception PDU:
Error Code: function code corresponding to the request with the most significant bit set.
Exception Code: code specifying the exception.
A transaction can be viewed in figure 2.1.
Request PDU:
Function Code Function Data
(1 byte) (n bytes)
Response PDU:
Function Code Response Data
(1 byte) (n bytes)
Figure 2.1: Modbus transaction
The function code field specifies the kind of service or function requested to the server (reading, writing, etc.).
For the list of available functions to access data, refer to item 7.1.
According to the protocol, each function is used to access a specific type of data. Table 2.1 contains the basic
types defined in the specification.
Table 2.1: Modbus data type
Name Size Access
Discrete Input 1 bit Read Only
Discrete Output (Coils) 1 bit Read and Write
Input Registers 16 bits Read Only
Holding Registers (Registers) 16 bits Read and Write
Each implantation of the Modbus protocol can add to the PDU specific data for the proper processing of the
messages through the interface used.
SSW900 | 8

MODBUS COMMUNICATION INTRODUCTION
2.2 MODBUS RTU
Two transmission modes are defined in the Modbus protocol specification for the serial interface: ASCII and
RTU. These modes define the way the message bytes are transmitted. It is not possible to use the two trans-
mission modes in the same network. The SSW900 soft-starter uses only the RTU mode for the telegram trans-
mission.
It allows up to 247 slaves, but only one master.
It adds to the Modbus PDU an address and error-checking field. The association of these fields to the PDU is
called ADU (Application Data Unit).
Modbus RTU telegram format:
•Address: used to identify the slave.
•PDU: Modbus PDU.
•CRC: field for checking the transmission errors.
The master initiates the communication sending a byte with the address of the slave to which the message is
destined. When sending the answer, the slave also initiates the telegram with its own address. The master can
also send a message to the address 0 (zero), which means that the message is destined to all the slaves in the
network (broadcast). In that case, no slave will answer to the master.
The last part of the telegram is the field for checking the transmission errors. The used method is the CRC-
16 (Cycling Redundancy Check). This field is formed by two bytes; where first the least significant byte is
transmitted (CRC-), and then the most significant (CRC+). The CRC calculation form is described in the protocol
specification.
In the RTU mode there is no specific character that indicates the beginning or the end of a telegram. The
indication of when a new message begins or when it ends is done by the absence of data transmission in the
network, for a minimum period of 3.5 times the transmission time of a data byte (11 bits). Thus, in case a
telegram has initiated after the elapsing of this minimum time, the network elements will assume that the first
received character represents the beginning of a new telegram. And in the same manner, the network elements
will assume that the telegram has reached its end when after receiving the telegram elements, this time has
elapsed again.
If during the transmission of a telegram the time between the bytes is longer than this minimum time, the telegram
will be considered invalid because the frequency inverter will discard the bytes already received and will mount
a new telegram with the bytes that were being transmitted.
For communication rates higher than 19200 bit/s, the used times are the same as for that rate. The next table
shows us the times for different communication transmission rates:
Table 2.2: Communication rates and the time periods involved in the telegram transmission
Baud rate T11bits T3.5x
1200 bits/s 9.167 ms 32.083 ms
2400 bits/s 4.583 ms 16.042 ms
4800 bits/s 2.292 ms 8.021 ms
9600 bits/s 1.146 ms 4.010 ms
19200 bits/s 573 µs 2.005 ms
38400 bits/s 573 µs 2.005 ms
57600 bits/s 573 µs 2.005 ms
•T11bits = Time for transmitting one byte of the telegram.
•T3.5x= Minimum interval to indicated beginning and end of a telegram (3.5 x T11bits).
SSW900 | 9

INTERFACE DESCRIPTION
3 INTERFACE DESCRIPTION
The SSW900 soft-starter has two Slots for accessories (Figura 3.1). Parameters S3.5.1 and S3.5.2 present
which accessory was recognized by Slot.
The accessories can be connected to any Slot, but only one type of each communication accessory is allowed.
Read the user’s manual of the SSW900 soft-starter before installing or using this accessory.
Slot 1
Slot 2
Figure 3.1: Slots for accessories
The SSW900 soft-starter uses the RS485 accessory to provide a Modbus RTU interface for communication.
Characteristics of this interface are described next.
3.1 RS485 ACCESSORY
SSW900-CRS485-W:
•Supplied items:
–Installation guide.
–RS485 communication module.
3.2 CONNECTOR
The accessory for RS485 communication has a connector (X20) for network connection. The connector pinout
is presented in table 3.1.
SSW900 | 10