DigiTrace TCONTROL-CONT-03 User manual
DigiTrace TCONTROL-CONT-03
Compact microprocessor controller
Régulateur compact géré par microprocesseur
Kompakter Mikroprozessorregler
INSTALL-160 Rev. 1
Modbus Manual
Notice Modbus
Modbus-Anleitung
2013-05-21/00521759
Contents
1 Introduction 5
1.1 Preface ........................................................................................................ 5
1.2 Typographical conventions ....................................................................... 5
2 Protocol description 7
2.1 Master-Slave principle ............................................................................... 7
2.2 Transmission mode (RTU) ......................................................................... 7
2.3 Device address ........................................................................................... 8
2.4 Timing of the communication ................................................................... 8
2.5 Structure of the data blocks ................................................................... 11
2.6 Function codes ......................................................................................... 12
2.6.1 Read n words ............................................................................................. 12
2.6.2 Write one word ........................................................................................... 13
2.6.3 Write n words ............................................................................................. 14
2.7 Transmission format (integer, float and text values) ............................. 15
2.8 Checksum (CRC16) .................................................................................. 17
2.9 Error processing ...................................................................................... 18
3 RS485 interface 19
3.1 Connection diagram ................................................................................ 19
3.2 Configuration ............................................................................................ 20
4 Modbus addresses 21
4.1 Process data ............................................................................................ 21
4.2 Set point values ........................................................................................ 22
4.3 Controller parameters ............................................................................. 23
4.4 Configuration ............................................................................................ 23
4.5 Commands ............................................................................................... 24
4.6 RAM memory ............................................................................................ 25
Contents
5
1 Introduction
1.1 Preface
This operating manual is addressed to the system manufacturer with adequate
technical background and PC related knowledge.
Please read this operating manual prior to commissioning the device. Keep
the manual in a place accessible to all users at all times. Your comments are
appreciated and may assist us in improving this manual.
All necessary settings are described in this operating manual. Should
problems be encountered during commissioning, please refrain from carrying
out any manipulations that are not described in the manual. Any such
intervention will jeopardize your warranty rights. Please contact the nearest
subsidiary or the head office.
1.2 Typographical conventions
Warning signs:
Caution
Note signs:
Note
Reference
Number types:
Hexadecimal
number
A
This symbol is used when there may be damage to equipment or
data if the instructions are ignored or not followed correctly!
H
This symbol is used when your special attention is drawn to a
remark.
v
This symbol refers to further information in other manuals,
chapters or sections.
0x0010 A hexadecimal number is identified by „0x“ preceding the actual
number (here: 16 decimal).
1 Introduction
6
7
2 Protocol description
2.1 Master-Slave principle
Communication between a master (e.g. PC) and a slave (e.g. measuring and
control system) using Modbus takes place according to the master-slave
principle, in the form of data request/instruction - response.
The master controls the data exchange, the slaves only have a response
function. They are identified by their device address.
2.2 Transmission mode (RTU)
The transmission mode used is the RTU mode (Remote Terminal Unit). Data is
transmitted in binary format (hexadecimal) with 8 bits. The LSB (least
significant bit) is transmitted first. The ASCII operating mode is not supported.
Data format The data format describes the structure of a character transmitted. The
following data format options are available:
Master
Slave 1 Slave 2 Slave n
Data word Parity bit Stop bit
1/2 bit
Number of
bits
8 bits — 1 9
8 bits even 1 10
8 bits odd 1 10
8 bits — 2 10
2 Protocol description
8
2.3 Device address
The device address of the slave can be set between 0 and 254. Device
address 0 is reserved.
There are two different forms of data exchange:
Query Data request/instruction by the master to a slave via the corresponding device
address.
The slave addressed responds.
Broadcast Instruction by the master to all slaves via the device address 0 (e.g. to transmit
a specific value to all slaves).
The connected slaves do not respond. In such a case, the correct acceptance
of the value by the slaves should be checked by a subsequent readout at each
individual slave.
Data request with the device address 0 is meaningless.
2.4 Timing of the communication
Start and end of a data block are marked by transmission pauses. The
maximum permitted interval between two consecutive characters is three
times the transmission time required for a single character.
The character transmission time (time required to transmit one single
character) depends on the baud rate and the data format used (stop bits and
parity bit).
For a data format of 8 data bits, no parity bit and one stop bit, this is:
character transmission time [ms] = 1000 * 9 bit/baud rate
For the other data formats, this is:
character transmission time [ms]
= 1000 * (8 bits+parity bit+stop bit(s)) bit/baud rate
H
A maximum of 31 slaves can be addressed via the RS485 interface.
9
2 Protocol description
Timing
Example Marker for end of data request or end of response for a 10/9 bit data format
Waiting time = 3 characters * 1000 * 10 bit/baud rate
Data request from master
transmission time = n characters * 1000 * x bit/baud rate
Marker for end of data request
3 characters * 1000 * x bit/baud rate
Processing of data request by the slave (250ms)
Response of the slave
transmission time = n characters * 1000 * x bit/baud rate
Marker for end of response
3 characters * 1000 * x bit/baud rate
Baud rate [baud] Data format [bit] Waiting time [ms]
(3 characters)
38400 10 0.79
90.71
19200 10 1.57
91.41
9600 10 3.13
92.82
2 Protocol description
10
Timing
scheme
A data request runs according to the following timing scheme:
t0End marker = 3 characters
(time depending on the baud rate)
t1This time depends on the internal processing.
The maximum processing time is 250 ms.
The minimum response time, which can be set is required by the RS485
interface in the master, to be able to switch over the interface drivers from
transmit to receive.
t2This time is needed by the slave to change from transmit back to receive.
The master has to observe this waiting time before presenting a new data
request. This time must always be observed, even when the new data
request is directed to another device.
RS485 interface: t2= 10ms
No data requests from the master are permitted during t1and t2 and during
the slave response time. Data requests made during t1and t2are ignored by
the slave. Data requests during the response time will result in the invalidation
of all data currently on the bus.
H
A minimum response time can be set in the device under the menu
point item „Interface“. This preset time is the minimum waiting time
before an answer is transmitted (0…500 ms). If a smaller value is set,
then the response time may be longer than the preset value (internal
processing takes longer), the device answers as soon as internal
processing is completed. The preset time of 0 ms means that the
device responds at the maximum possible speed.
Master
Slave
Data request
Response
t
Data request
t
0t1t2
t0
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