Linak TECHLINE LA35 User manual

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LINAK.COM/TECHLINE
Modbus option for LA35, LA36 and LA37
Installations guide

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Contents
Introduction ............................................................................................................................................3
Concept ................................................................................................................................................3
MODBUS RTU System..............................................................................................................................3
Safety instructions...................................................................................................................................4
Installation...........................................................................................................................................5
Connection, cables and plugs ..................................................................................................................5
Installation rules......................................................................................................................................7
Reverse polarity protection ......................................................................................................................9
MODBUS RTU Functional Description............................................................................................. 11
Implementation class.............................................................................................................................11
Unicast/broadcast .................................................................................................................................12
Response time.......................................................................................................................................12
Error checking.......................................................................................................................................13
Message format ....................................................................................................................................13
Register-parameter mapping..................................................................................................................14
Data formats.........................................................................................................................................15
Function codes......................................................................................................................................16
Exceptions ............................................................................................................................................19
Typical Use Cases ..............................................................................................................................20
Configuration........................................................................................................................................20
Run to target ........................................................................................................................................20
Run to predefined positions...................................................................................................................21
Ramp down before target...................................................................................................................... 22
Activation of multiple actuators.............................................................................................................22
Retrieval of service data.........................................................................................................................23
Customisation of MODBUS register mapping .........................................................................................23
BusLink Configuration Software ..................................................................................................... 25
Screen nr. 1: “Program initialisation” ..................................................................................................... 25
Screen nr. 2: “Configuration tab”...........................................................................................................26
Screen nr. 3: “Manual run”....................................................................................................................28
Screen nr. 4: ”Firmware” .......................................................................................................................29
Screen nr. 5: “Service counters”.............................................................................................................30
Troubleshooting ................................................................................................................................31
Problem: The master does not get any response from the actuator..........................................................31
Problem: The master does not reliably get responses from the actuator(s) ...............................................31
Problem: The master receives a ‘Slave Device Failure’ from the actuator..................................................31
Problem: The master receives an exception response from the actuator...................................................31
Problem: The actuator does not move after a run-command ................................................................... 32
Problem: BusLink PC tool can not communicate with the actuator..........................................................32
Problem: Actuator firmware is corrupted e.g. due to upgrade problem ....................................................33
Declaration of incorporation of partly completed machinery ....................................................34
Appendix A – Register Map .............................................................................................................35
Addresses...........................................................................................................................................44

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Introduction
The RS485 MODBUS RTU option is a serial communication interface between the actuators and a control system.
The MODBUS interface can directly communicate with a PLC with a MODBUS module or a PC through an external
USB to RS485 interface box.
This document describes how to install, configure and use an actuator with embedded MODBUS RTU serial
communication.
Basic serial bus communication knowledge is a prerequisite for using and understanding the below documentation.
Supporting literature:
[1] MODBUS over serial line specification and implementation guide V1.02 (LINK)
[2] MODBUS Application Protocol Specification V1.1b (LINK)
[3] BusLink configuration software (if you do not have BusLink please contact your local LINAK office)
Concept
Modbus RTU System
Universally recognised and widely used, the MODBUS RTU fieldbus is still an essential, open communications
standard, supported by a large number of products on the market today.
In the MODBUS network any MODBUS Master can be connected to one or several LINAK LA35/LA36 Actuators
with MODBUS interface. The topology is a serial bus-system with actuators including derivation cable connected
to a trunk cable through passive TAPs. One master PLC or PC can be connected to the serial bus to control and
supervise the actuator slaves. The actuators might potentially be mixed with other 3rd party MODBUS slaves.
PLC
Modbus RTU Master
(incl. terminator)
Passive TAPs Terminator
Derivation
cable/Stub
Trunk cable
LINAK Actuators
Modbus RTU slaves

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At the physical protocol level, the RS-485 (TIA/EIA-485) two-wire interface is used, which supports half-duplex
communication between the master and one or more slaves. Inter-communication between slaves is not possible
and a slave will never transmit data without receiving a request from the master.The master (incl. terminator) can
be connected at the end of the cable as shown in the figure above.
Alternatively connection of the master anywhere in-between two of the slaves is acceptable as well. As shown
below the terminator is then moved to the end of the trunk cable.
Safety instructions
Be aware of the following symbols throughout the installation guide:
Recommendations
Failing to follow these instructions can result in the actuator suffering damage or being ruined.
Additional information
Usage tips or additional information that is important in connection with the use of the actuator.
Be aware that a lot of test and quality activities have been performed to ensure the functionality and
safe use of the product. As with other electronic equipment the MODBUS option has a finite failure
rate. To ensure that one failure does not lead to an unsafe state the microcontroller monitors critical
components (1. failure surveillance). It is still possible to run the actuator but it is of utmost importance
that the user reacts upon these events to maintain 1. failure safety (i.e. polling of relevant MODBUS
registers to identify the reason for last stop) – see Troubleshooting page 32 (Problem: The actuator does
not move after a run-command).
PLC
Modbus RTU Master
(excl. terminator)
Terminator Terminator
Trunk cable
Derivation
cable/Stub
Passive TAPs
LINAK Actuators
Modbus RTU slaves

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Installation
Connection, cables and plugs
The actuator data and power cables are separate from each other and pre-mounted on the LA35/LA36/LA37
Actuators.
Power cable
Standard LA35, LA36 and LA37 power cables are used. The power cable is an open-end flying leads version.
The following issues must be considered when extending the power cable:
There are no specific requirements for the power cable itself other than it of course needs to be dimensioned to
handle the maximum voltage drop for the actuator with the longest cable distance from the power supply. In
terms of choosing the right power cable other issues must also be clarified, i.e.:
• The worst case current consumption for the individual actuator
• If it is specified that more than one actuator should run simultaneously
In other words the goal is to select cable dimensions, which ensure, that the input voltage of all bus actuators is
within the specified limits under the selected worst case operating conditions.
Data cable
The data derivation cable ends in a standard M12 x 1 connector (Male, A-coded, 5-position). The data cable
mounted from the factory must always be used.
The connector pin layout has been chosen to enable use of standard DeviceNet M12 cables, passive TAPs
(T-pieces) and terminators.

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Even though the EIA-485 specification states that Ais the inverting signal and Bis the non-
inverting signal, several RS485 transceiver manufacturers specify the opposite, which is a widespread
misunderstanding.
As LINAK only supplies the derivation cabling from actuator to the nearest TAP in the trunk, the longer distance
cabling that interconnects the individual TAPs is the responsibility of the customer/system integrator.
The following cable characteristics must be fulfilled when selecting the trunk cabling:
Electrical requirements according to TSB89, Application Guidelines for TIA-EIA-485-A which is typical:
• 24 AWG shielded twisted pair
• 120 Ω characteristic impedance
• Capacity less than 40 pF/meter
• Drain wire as common signal reference
Pin Signal
1 Common RS485 signal reference +
shield of the cable
2 Reserved for future use
3 Reserved for future use
4 RS485 non-inverting signal – RS485_B
(aka TxD+/RxD+)
5 RS485 inverting signal – RS485_A (aka
TxD-/RxD-)

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Installation rules
Grounding arrangements
The RS485 Signal Common must be connected directly to protective ground, at one point only for the entire bus.
Generally this point is to be chosen on the master device or on its TAP, preferably using the power supply GND
(negative supply). It is highly recommended that the RS485 interface on the master is chosen to be an isolated
type.
It is not allowed to connect the RS485 Signal Common to the power supply GND at the actuator nodes.
Doing so will cause high ground currents to flow in the « Common » circuit.
Line termination
A reflection in a transmission line is the result of an impedance discontinuity that a travelling wave sees as it
propagates down the line.
To minimise the reflections from the end of the RS485-cable it is required to place a Line Termination (LT) near
each of the 2 ends of the Bus.
The termination is made with a 120 Ohms (0.25 W) resistor (see figure below).
Line biasing
No line biasing is necessary for the LINAK MODBUS actuators to function, as their isolated RS485-transceivers
are true fail-safe, meaning that they correctly handle an idle bus (no enabled driver on the bus).
Cable length and number of slaves
Even though a MODBUS master can logically address up to 247 nodes in a multipoint serial line there are several
parameters that have an influence on the maximum number of slaves in a system.

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The RS485 standard basically specifies a system consisting of 32 slaves without the use of repeaters. Modern
transceivers allow for even more, as their bus load is less than the maximum allowed by the RS485 standard.The
LINAK MODBUS actuators use such modern transceivers, theoretically supporting up to 256 nodes. In real life this
number is reduced by the below listed operating conditions:
• The baud rate
• The total length of the trunk cable
• The total length of the derivation cables
• The quality of the cabling
• The functionality i.e. the poll rate
Based on our tests, a bus string with a master, 32 LINAK actuators and no 3’rd party slaves will work under the
following conditions:
• Baud rate: Up to 19200
• Data cable: Following the guidelines in the following section DATA cable
• Derivation cables: Standard LINAK cable supplied with MODBUS actuator, not extended
• Termination: In both ends of string
• Total string length: 1000 m
If your MODBUS system either:
• includes more than 32 actuators
• the trunk cable exceeds 1000 m
• the derivation cables are extended
• includes 3rd party slaves
..then you have to test if the installation needs repeaters or other actions to provide a stable communication level.
Wiring in general
Be careful not to run any AC cabling in parallel with the wiring for the actuator system as this will create
a noisier environment.
Power up rules
• It is preferable not to have power on the power line when you connect or disconnect
the actuators.
• Fuse selection: It is recommended to install a fuse for each actuator in a string (prevents
a dead string (series of actuators) in case of an error (e.g. short circuit)). Alternatively, a fuse for
each power supply must be installed. It is also recommended to use a current limited power supply.

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Reverse polarity protection
In the case of reversing the polarity of the power to the actuator, a protection diode gets into action (short cir-
cuiting the input voltage).The result is a very high current. As the protection diode has a limited current handling
capability, the fuse mentioned above must open in order to limit the duration of the short circuit.
The following table shows the allowed reverse current at different current pulse durations. The duration of the
pulse is determined by the time it takes for the fuse to open:
Pulse duration (ms) Max allowable current (A)
10
120
50
100
100
90
500
80
1000
80
Infinite
7
If the values in the above table are exceeded, the actuator will take permanent damage.
This is used when selecting the power supply and the fuse types for a string of actuators. The power
supply must be a current limiting type and the maximum operating time* for the selected fuse must be
known at the current limit of the power supply. (For further explanation read the following examples):
Example 1
The selected power supply has a current limit of 40A. The selected fuse protecting each actuator has a nominal
rating of 10A and a guaranteed opening time at 400% rated of maximum 400ms. If the actuator is connected
with reverse polarity, the fuse (and the reverse polarity diode in the actuator) will see 40A of current. At this level,
the current will be interrupted after 400ms maximum.We can see from the table that this is OK, as a current pulse
of up to 80A with duration of 500ms is allowed.

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Example 2
The selected power supply has a current limit of 100A. The selected fuse protecting each actuator has a nominal
rating of 10A and a guaranteed opening time at 1000% rated of maximum 150ms. If the actuator is connected
with reverse polarity, the fuse (and the reverse polarity diode in the actuator) will see 100A of current. At this
level, the current will be interrupted after 150ms maximum. We can see from the table that this is not OK, as a
current pulse of up to 100A is only allowed to have a duration of 50ms.
* Usually stated at 150%, 210%, 275%, 400% and 1000% of the rated current.
When using soft-stop on a DC-motor, a short peak of higher voltage will be sent back towards the power
supply. It is important when selecting the power supply, that it does not turn off the output, when this
backwards load dump occurs.

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Modbus RTU Functional Description
Implementation class
The LINAK MODBUS protocol is implemented conforming to the “basic slave” implementation class as described
in document [1]. The following options have been implemented:
Parameter Options Default value Remarks
Adressing
Configurable from 1 to
246
247 (= un-assigned) Configured by BusLink
software
Broadcast Yes
Baud rate 9.6 kBaud - 115.2 kBaud 19.2 kBaud Configured by BusLink
software
Parity Even, odd, no-parity Even Configured by BusLink
software
Stop Bits 1, 2 1 Configured by BusLink
software. Notice that a
No-parity setting requires
2 stop bits
Mode RTU - Not configurable
Electrical Interface RS485 2W-cabling - Not configurable
Connector Type M12 - Not configurable

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Broadcasting
The master broadcasts a message to address “0”, which means that the information is for all slave devices on
the network. These stations execute the order without transmitting a response.
Unicast/broadcast
MODBUS is a single master system, which means that only one master can be connected at any single point in
time. Two modes of communication are possible, Unicast and Broadcast.
Request/response (unicast)
The requests from the master are addressed to a given slave. The master then waits for the response from the
slave which has been interrogated. In this mode the transaction consists of 2 messages: a request from the
master and a response from the slave.
Response time
The slave device will respond on each valid MODBUS request from the master within a time which is dependent
on the setting of parameter ‘MODBUS Response Delay’ (Input Register 59). With a default parameter value (3
ms) the max. response time is 18 ms (3 + 15 ms) – when increasing the parameter value worst case is 115 ms
(100 + 15 ms).

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Modbus message timing:
Master request
Slave processing &
Slave response
Master
Start of
transaction
The MODBUS response timeout setting of the master should be set to a value larger than the calculated
max. response time.
Error checking
MODBUS RTU networks employ two methods of error checking:
1. Parity checking of each data character (even, odd, or no parity)
2. Frame checking within the message frame (Cyclical Redundancy Check)
Parity checking
A LINAK MODBUS device can be configured for even or odd parity, or for no parity checking.This determines how
the parity bit of the character’s data frame is set. If even or odd parity checking is selected, the number of 1 bits
in the data portion of each character frame is counted. Each character in RTU mode contains 8 bits. The parity
bit will then be set to a 0 or a 1, to result in an even (even parity), or odd (odd parity) total number of 1 bits.
The use of ‘no parity’ requires 2 stop bits.
Frame checking
RTU Mode message frames include an error checking method that is based on a Cyclical Redundancy Check
(CRC). The error-checking field of a message frame contains a 16-bit value (two 8-bit bytes) that contains the
result of a Cyclical Redundancy Check (CRC) calculation performed on the message contents.
Message format
Any MODBUS message consists of the basic fields shown below: Slave address (Addr), Function code (Function),
up to 252 data bytes (Data) and a calculated 16 bit checksum (CRC).
Byte 0 Byte 1 Byte 2 .. N Byte N+1, N+2
Addr
Function Data CRC

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Messages start with a silent interval of at least 3.5 character times – at the actual communication baud rate.The
first field transmitted is the device address. Following the last transmitted byte, a similar interval of at least 3.5
character times marks the end of the message. A new message can begin after this interval.
Address field
The address field Addr is one byte long. Valid slave addresses are 1 – 246. Value 0 and value 247 to 255 is
reserved for special purposes. A master addresses a slave by placing the slave address in the Addr field of the
message. When the slave responds it places its own address in the Addr field to let the master know which slave
is responding.
Each slave device must have assigned a unique address (from 1-246) so that it can be addressed
independently from other nodes. Value 0 is reserved for broadcast messages which all slaves recognise.
Function field
The function field Function is one byte. Supported MODBUS functions are 3, 4, 6, 16. When a message is sent
from the master to a slave, the function field code tells the slave what kind of action to perform.
When the slave responds to the master, it uses the function field to signal either a normal, error-free response or
an exception response. For a normal response the slave simply echoes the original function code. For an exception
response the slave returns a code that is equivalent to the original function code with the most significant bit
set. In addition the slave adds a unique code into the data field of the message telling the master what kind of
error occurred.
Data field
The data field is of varying length. The data field of the message sent from the master to the slave contains
additional information which the slave must use to take the action requested by the function field. This can
include items like register addresses, quantity of register to handle, and the count of actual data bytes in the
message.
CRC field
The CRC field is 2 bytes long. The CRC value is calculated by the transmitting device, which appends it to the
end of the message. The receiving device recalculates a CRC during receipt or the message and compares the
calculated value to the actual value received in the CRC field. In the case of a difference an exception response
is returned.
Register-parameter mapping
All data addresses in MODBUS messages to LINAK actuators are referenced to zero. The input register known as
e.g.‘Input Register 30002’ in a programmable controller is addressed as register 1 in the Addr field of a MODBUS
message. The function code of the message already specifies an ‘Input Register’ operation and therefore the
‘3xxxx’ reference is implicit.

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In the same way the holding register known as e.g. ‘Holding register 40008’ is addressed as register 7 in the Addr
field of the message, together with a relevant Holding Register function code.
All MODBUS registers are default mapped to a specific actuator parameter. To optimise communication throug-
hput when reading or writing non-contiguous register sets, it is possible to re-define this mapping (as described
later in this guide).
Data formats
Application information communicated between MODBUS master and slave is organised as one or more 16-bit
Registers. Different datatypes are mapped into theses addressable registers. The type of any parameter value
embedded into the MODBUS message has to be recognised according to the register/parameter tables in Appen-
dix A. LINAK MODBUS devices support the following datatypes (illustrated by single register write-message
examples):
Short integer register (U8)
Status bytes and small integer values are stored in MODBUS registers where only half of the register is utilised.
Integer values from 0 to 255 are stored in the least significant byte of the register.
Unsigned integer register (U16)
Integer values from 0 to 65,535 are stored in the normal 2-byte MODBUS register. The most significant byte of
the value is sent first.
Signed integer register (S16)
Integer values from -32,768 to 32,767 are stored in the normal 2-byte MODBUS register. The most significant
byte of the value is sent first.
Byte 0 Byte 1 Byte 2 .. 5 Byte 6, 7
Addr
Function Register address Register data CRC
MSB LSB N/A U8
Byte 0 Byte 1 Byte 2 .. 5 Byte 6, 7
Addr
Function Register address Register data CRC
MSB LSB U16-MSB U16-LSB
Byte 0 Byte 1 Byte 2 .. 5 Byte 6, 7
Addr
Function Register address Register data CRC
MSB LSB S16-MSB S16-LSB

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Long integer registers (U32)
Some integer values used by the actuator are larger than 65,535, which is the largest number that can be stored
in a single MODBUS register. In these cases, the unsigned value is stored in two consecutive integer registers
enabling values up to 4,294,967,295.These “long integer” registers are potentially accessed using the MODBUS
functions 3, 4, and 16 (see below). The most significant word is stored in the lower register (sent first), and the
least significant word is stored in the higher register.
Function codes
The LINAK actuator supports a subset of the standard MODBUS RTU function codes to provide access to the
internal actuator parameters and functions.
The LINAK MODBUS protocol does not support the Diagnostic function (function code 08). As a more general
approach, the MODBUS master – and the BusLink service tool – can read a large amount of service counter input
registers.
Function code 3 – Read Holding Registers
Function code 3 is used to read one or more holding registers in the actuator, referenced inAppendixA. When the
master access a register that is not supported by the slave it responds with an exception message.
The register address in this context is without ‘4xxxx’ identification. E.g. the ‘Target Position’ holding register is
read via register address 1 – in the PLC often referenced as 40002.
Broadcast is not supported.
Request message:
In the response message the requested values are delivered to the master.The data bytes are organised according
to data type as explained above.
Response message:
Byte 0 Byte 1 Byte 2 .. 7 Byte 8, 9
Addr
Function Register address Register data CRC
MSB LSB U32-
MSB
U32-
LSB
Addr Function Register address Register count CRC
Slave
Address
Function
Code (=3)
Starting
Address
High
Starting
Address
Low
No. of
Registers
High
No. of Regis-
ters Low
Addr Function Data CRC
Slave
Address
Function
Code (=3)
Byte Count Data byte 1 .. N

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Function code 4 – Read Input Registers
Function code 4 is used to read one or more input registers in the actuator, referenced in Appendix A. When the
master accesses a register that is not supported by the slave, it responds with an exception message.
The register address in this context is without ‘3xxxx’ identification. E.g. the ‘Distance from Target’ input register
is read via register address 3 – in the PLC often referenced as 30004.
Broadcast is not supported.
Request message:
In the response message the requested values are delivered to the master.The data bytes are organised according
to data type as explained above.
Response message:
Function code 6 – Write single Holding Register
Function code 6 is used to write a new value to a holding register of the actuator, referenced in Appendix A.When
the master accesses a register that is not supported by the slave or when it tries to write a value outside defined
boundaries the slave responds with an exception message.
The register address in this context is without ‘4xxxx’ identification, e.g. meaning address 0 equals register
40001.
Broadcast is supported (but any response – including exceptions - is discarded).
Request message:
Addr Function Register address Register count CRC
Slave
Address
Function
Code (=4)
Starting
Address
High
Starting
Address
Low
No. of
Registers
High
No. of Regis-
ters Low
Addr Function Data CRC
Slave
Address
Function
Code (=4)
Byte Count Data byte 1 .. N
Addr Function Register address Register data CRC
Slave
Address
Function
Code (=6)
Address
High
Address
Low
New Value
High
New Value
Low

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The normal response is an echo of the request message.
Response message:
Function code 16 – Write Multiple Holding Registers
Function code 16 is used to write one or more holding registers in the actuator, referenced in Appendix A. When
the master accesses a register that is not supported by the slave it responds with an exception message.
The register address in this context is without ‘4xxxx’ identification, e.g. meaning address 0 equals register
40001.
Multiple registers are written as an entity with commands executed as the final stage.That means, if e.g. Holding
Register 1, 2 and 3 (Target Position, Command-Remote and Max Speed) are written in one single command then
the actuator will start running towards the new position with the new speed.
Broadcast is supported (but any response – including exceptions - is discarded).
Request message:
The normal response message returns the slave address, function code, starting address and the quantity of
registers written.
Response message:
Addr Function Register address Register data CRC
Slave
Address
Function
Code (=6)
Address
High
Address
Low
New Value
High
New Value
Low
Addr Function Register address Register count Register
Data
CRC
Slave
Address
Function
Code (=3)
Starting
Address
High
Starting
Address
Low
No. of
Registers
High
No. of
Registers
Low
Byte
Count
New Value
1 .. N
Addr Function Register address Register count CRC
Slave
Address
Function
Code (=16)
Starting
Address
High
Starting
Address
Low
Register
Count High
Register
Count
Low

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Exceptions
When a MODBUS master transmits a request to a slave the expected behaviour is that the slave responds with a
normal response. But several error scenarios are possible:
• The slave does not receive the request due to a communication error. No response is returned;
the master will process a time-out and eventually repeat the request.
• The slave receives the request but detects a parity or CRC communication error. No response is
returned; the master will process a time-out and eventually repeat the request.
• The slave receives the request without a communication error but cannot handle it. The slave
will in that case return an exception response informing the master about the nature of the error.
Exception response message:
Exception codes are:
Addr Function Error CRC
Slave
Address
Function
Code
+80 hex
Error Code
Exception
Code
Definition Description
01 Invalid Function The message received is not an allowable action
02 Illegal Data Adress The register address(es) referenced in the function-dependent data
section of the message is not valid
03 Illegal Data Value The data value of the referenced address is not within limits
04 Slave Device
Failure
The addressed device is not able to process a valid message due to a
bad device state

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Typical Use Cases
In this section further descriptions of how to communicate with the LINAK LA35/LA36/LA37 Actuators are shown.
The examples are typical user scenarios and application solutions. All examples include references to registers,
which are further described in details in Appendix A.
Configuration
Before integration into a MODBUS system a few parameters of the actuator have to be checked and eventually
changed.This preparation is done by use of the BusLink PC tool (the tool is described in details later) and guaran-
tees that the actuator is able to execute basic functionality. Further fine-tuning may be required to fulfil system-or
application requirements.
Parameters to be verified by BusLink:
Run to taget
Before you move the actuator to any new position you have to verify that some general prerequisites are fulfilled.
Timing (e.g. when the actuator is still moving), environment conditions and errors might mean that the actuator
is in a state where further operation is not possible.
General run-prerequisites:
*IR = Input Register, HR = Holding Register
Parameter Description
Address Set the MODBUS device address to a unique value between 1 and 246.
Baudrate The baudrate parameter is set to the communication speed required by the PLC/
system.
Parity The parity parameter is set to the value required by the PLC/system.
Stopbits The stopbits parameter is set to the value required by the PLC/system.
Current limit in Depending on the load in the specific application it might be necessary to adjust
this parameter. If the motor current exceeds this limit, the actuator will not move.
Current limit out Depending on the load in the specific application it might be necessary to adjust
this parameter. If the motor current exceeds this limit, the actuator will not move.
Max speed Set the actuator speed according to application requirements.
Step Register * Action
1 IR 4 ‘Status Register 1, bit 4 (Ready)’ has to be = 1.
2 IR 4 ‘Status Register 1, bit 9 (LOCAL connected)’ has to be = 0.
3 IR 4 ‘Status Register 1, bit 10 (Position Valid)’ has to be = 1.