KROHNE IFC-300 User Manual
Supplementary instructions
Supplementary instructions
IFC 300
IFC 300
IFC 300IFC 300
Supplementary instructions Supplementary instructions
Signal converter for electromagnetic flowmeters
Description of Modbus interface
Description of Modbus interface
Description of Modbus interfaceDescription of Modbus interface
Electronic Revision: ER 3.3.xx (SW.REV. 3.3x)
Modbus version 1.2.x
© KROHNE 07/2010 - 4000410703 - AD Modbus IFC 300 R03 en
CONTENTS
IFC 300
1 Important information 3
2 Technical data 4
2.1 General technical data .....................................................................................................4
2.2 Technical data of the Modbus interface (acc. to EIA standards) ..................................... 4
3 Connection in bus systems 5
4 Local configuration 6
5 Electrical connection 7
6 Modbus protocol 8
6.1 General information concerning the protocol ................................................................. 8
6.2 RTU frame format............................................................................................................. 8
6.3 Addressing........................................................................................................................ 9
6.4 Overview of supported functions...................................................................................... 9
6.5 Device identification on the Modbus interface............................................................... 10
6.6 Coil registers .................................................................................................................. 10
6.6.1 Converter controls ................................................................................................................ 10
6.6.2 Counter controls ................................................................................................................... 11
6.6.3 Start calibration functions .................................................................................................... 11
6.7 Input registers ................................................................................................................ 12
6.8 Holding registers............................................................................................................ 14
6.8.1 Counter parameters ............................................................................................................. 14
6.8.2 Process input filter parameters ........................................................................................... 15
6.8.3 Modbus parameters.............................................................................................................. 17
6.9 Diagnostics ..................................................................................................................... 17
6.10 Calibration procedures................................................................................................. 18
6.10.1 Zero Flow Calibration.......................................................................................................... 18
6.10.2 Coil Temperature Calibration ............................................................................................. 19
6.10.3 Conductivity Calibration...................................................................................................... 20
7 Notes 21
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IFC 300
IMPORTANT INFORMATION 1
The flow converter with the RS485 interface card fitted, is able to communicate with an external
device (PC or other suitable computer system) using the Modbus protocol. This option allows
data exchange between PC or computer and single or multiple devices.
The bus configuration consists of one external device as a master and one or more converters as
slaves. For bus operation the device address (menu C5.8.1), baudrate (menu C5.8.2) and settings
(menu C5.8.3, C5.8.4, C5.8.5 & C5.8.6) must be set in the converter.
All devices connected to the bus, must have different unique addresses but the same baud rate
and settings.
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2 TECHNICAL DATA
2.1 General technical data
Interface RS485, galvanically isolated
Baud rate 1200, 2400, 4800, 9600, 19200, 38400, 57600 or 115200
Protocol Modbus RTU (available as a separate document on request)
Maximum participants on bus 32 per line, master included (may be extended by repeaters)
Coding NRZ bit coding
Address range Modbus: 1...247
Transmission procedure Half duplex, asynchronous
Bus access Master / slave
Cable Screened twisted pair
Distances Maximum 1.2 km / 3937 ft without repeater (dependant on
baud rate and cable specifications)
2.2 Technical data of the Modbus interface (acc. to EIA standards)
Kind of signal transmission Differential, 2-wire topology
Maximum number of
transmitter/receivers
Voltage range on converter input -7...+12 V
Maximum voltage on converter output 5V
Minimum voltage on driver output, max.
load
Maximum input current (off state) -20...+20 μA
Receiver input voltage -7...+12 V
Sensitivity of the receiver -200...+200 mV
Receiver input resistance >12kΩ
Short circuit current < 250 mA
Termination / polarization resistors
(if activated by the jumpers X5/X6)
32
U
>1.5V
diff
120 Ω / 560 Ω
IFC 300
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IFC 300
CONNECTION IN BUS SYSTEMS 3
For proper operation of Modbus in half duplex mode in single or multi-drop communication, it is
recommended that a termination resistor is applied to both ends of the data line. The simplest
form of termination is line-to-line resistor across the differential input.
In RTU mode the Modus protocol requires quiet periods on the communications bus for
synchronisation. It is therefore important that the Modbus is not allowed to "float", i.e.
unreferenced to 0 V, as this could lead to spurious signals due to noise pick-up. It is therefore
necessary to employ biasing resistors at one point on the bus network, normally the "end".
The Modbus converter has two conditions. Default is without termination and polarization. To get
the active termination and polarization the settings of jumper X5 and X6 on Modbus board must
be changed then. For detailed information see chapter "Electrical Connection".
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4 LOCAL CONFIGURATION
IFC 300
Converter Fct.
Display Description and settings
No.
C5.8.1 Slave Address Selects the Modbus address of the device.
C5.8.2 Baud Rate Selects the baud rate of the device.
C5.8.3 Parity Selects the parity.
C5.8.4 Data Format Selects the data format.
C5.8.5 Transmission Delay Selects the delay between receiving the last byte of a request and
C5.8.6 Stop Bits Selects the number of stop bits.
C5.8.7 Information Displays information about the device.
Range: 1..247 (default = 1)
Options:
1200 / 2400 / 3600 / 4800 / 9600 / 19200 (default) / 38400 / 57600 / 115200
Options:
Even (default) / Odd / No
Options:
Big Endian (default) / Little Endian
sending the first byte of the response.
Range: 0..40ms (default = 0ms)
Options:
1 (default) / 2
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IFC 300
ELECTRICAL CONNECTION 5
Terminals A and B of the converter are dependant on the options selected at order. Refer to the
standard handbook of the converter for connection details.
Modbus connections
Terminals Description
D- Signal A (D 0)
D Signal B (D 1)
C- Common 0 V
C Not connected
Jumper settings on the Modbus printed circuit board
Jumper position Description
X5 X6
1-2 1-2 With termination and polarization
2-3 2-3 Without termination and polarization
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6 MODBUS PROTOCOL
6.1 General information concerning the protocol
Using RTU (Remote Terminal Unit) format, data is transmitted as 8 bit binary characters. There
are no special characters to determine the start and end of a message frame.
Synchronization is achieved by a minimum silent period of at least 3.5 character times before the
start of each frame transmission and a maximum silent period of 1.5 character times between
characters in the same frame.
6.2 RTU frame format
The format of the query and response frames vary slightly depending upon the command
function. The basic form is outlined below.
Command function Frame format Description
IFC 300
Silent period 3.5 x T All transmissions must be preceded by a minimum silent
Slave address 8bits This is a single byte slave address which is transmitted
Function code 8bits This is an eight bit code in the range of 1...255 although
Register start address or
byte count when required
Number of points or data
bytes when required
8 bit byte count
16 bit address
n×8bits Number of points:
period of 3.5 x T, where T is the transmission time of a
single character. This can be calculated from the baud
rate, e.g. at 19.2 kb no parity with 1 stop bit (10 bits),
T=520µs.
first and must be in the range of 1...247. Address 0 is
reserved for a broadcast address which all slaves should
recognize, and therefore requires no response.
only 126 functions exist as the codes 129...255 represent
an error condition. An error condition occurs when the
addressed slave does not accept the command, in which
case it responds with the function code + 128, i.e. with its
MSB set to 1.
Register start address:
Register start address: for a query command that requires
Register start address:Register start address:
data to be returned, this field will contain the 16 bit start
address of the register (or data) to be returned.
Note that the converter uses protocol addresses.
Therefore the register address listed is the actual number
required in the Modbus command.
E.g:
E.g: to access input register 30006, the register start
E.g:E.g:
address is 30006dec = 7536hex.
Byte count:
Byte count: In general this is only present in frames that
Byte count:Byte count:
are transferring data, and has a value equal to the number
of bytes contained in the data field. The data field is limited
to a maximum of 250 bytes.
Number of points: for a query command that requires data
Number of points:Number of points:
to be returned, this field will contain the number of
registers to be returned regardless of their bit size.
Data bytes:
Data bytes: contains the data requested. The converter can
Data bytes:Data bytes:
use big endian format (MSB first) or little endian
format (LSB first).
CRC 16 bits This field contains a 16 bit CRC which is calculated on all
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the data bits of the message bytes.
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