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The protocol executes client (master) communication with arbitrary devices which supports a standard MODBUS RTU and ASCII in the versions of serial communication as well as MODBUS over TCP/IP. Moreover, it supports two extensionextensions:
- Byte mode - allows to work working with devices that get back the values of registers as 1 byte (in contrast with Modbus standard in which the register value is 2 bytes).
- Variable mode - allows to work working with devices that get back values of registers with different size as normal sizes than standard 2 bytes. It was implemented because of support the flowmeter FloBoss 103 made by Fisher Controls International (at this time a part of Emerson Process Management): 1-byte variables, 4-byte unsigned/signed integers, text strings of length 10,12,20,40 characters, 6-byte time stamp, and other.
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- Line category Serial (serial communication)
- Line category SerialOverUDP Device Redundant (serial communication).
- Line category RFC2217 Client (serial communication).
- Line category TCP/IP-TCP and TCP/IP-TCP Redundant (MODBUS over TCP/IP). Reserved TCP port 502 is used in common, but it is possible to use any other one according to the setting of the device. Number of The line number is not used, for example set the value e.g. to 1.
Note: For redundant systems, it is possible to enter multiple names addresses separated by commas.
Note: In the case of WAGO 750-8100 type PLC and communication via MODBUS TCP, it was necessary to set a small polling period (e.g. 1 second) in the time parameters of the station. In the case of a longer period (5 seconds), the connection was closed quite often by the PLC.
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A dialog window of of communication line configuration - Protocol parameters tab.
They influence some optional protocol parameters.
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Parameter | Meaning | Unit | Default value | ||||||
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| The parameter is implemented only for TCP/IP-TCP and TCP/IP-TCP Redundant line categories. The parameter activates the disconnection of the TCP connection after the execution of each read cycle, or after the value is written. The parameter was implemented due to problems with connection stability on mobile GPRS networks. | YES/NO | NO | ||||||
| Setting Tcp No Delay parameter to YES causes low-level socket option TCP_NODELAY being set, thus turning off the default packet coalesce feature. The parameter is implemented only for TCP/IP-TCP and TCP/IP-TCP Redundant line categories. | YES/NO | NO |
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- Communication protocol "Modbus Client".
- Station The station address is a decimal figure number mostly in the range of 1 up to 247. Address 0 is reserved as broadcast.
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Configuration dialog box - tab Parameter.
They influence some optional parameters of the protocol. Following The following station protocol parameters can be set:
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Parameter | Meaning | Unit | Default value | ||||||
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| Maximum count of request retries. If no reply returns after a request had been sent, the station will be in the status of a communication error. | s | 2 | ||||||
| Timeout before resending a request if no reply had not received. | s | 0.1 | ||||||
| Delay after sending the request before reading the response. | s | 0.1 | ||||||
| Timeout between reading the reply. | s | 0.1 | ||||||
| The maximum number of retries of the reply reading. | - | 20 | ||||||
| "Start silent interval" before the beginning of the transmission in RTU mode. | ms | 50 | ||||||
| "Stop silent interval" after ending of the transmission in RTU mode. | ms | 50 | ||||||
| Byte order in Little-endian mode for 4-byte variables. The individual options indicate in which bytes (1-lowest, 4-highest) the individual bytes from the communication will go:
| - | 2143 | ||||||
| Special byte mode of transmission in which the values of registers have a length of 1 byte and not 2 bytes as it is defined in Modbus protocol specification. | YES/NO | NO | ||||||
| Special variable mode of transmission in which the values of registers have variable lengths. The setting of Variable mode: Note 1: Variable and byte mode are incompatible and only one of them can be enabled. | OFF Little endian Big endian | OFF | ||||||
| Logging of detailed debug information about communication in the line log. | YES/NO | NO | ||||||
| Protocol mode: RTU or ASCII. Note: In the case of "MODBUS over TCP/IP", the parameter value is ignored and Protocol Mode=RTU is used. | RTU ASCII | RTU | ||||||
| Sets an address model of MODBUS protocol: MODBUS PDU data are addressed from 0 up to 65535. MODBUS data Model data are addressed from 1 up to 65536. Note: MODBUS PDU is a default value. If the MODBUS data Model is set, the object with the address X is addressed as X-1 in MODBUS PDU. After you change this parameter, restart a proper communication process. | MODBUS PDU MODBUS data Model | MODBUS PDU | ||||||
| Select a variant of the protocol in case of TCP/IP communication: "MODBUS TCP" is a variant of communication without control checksum. Safeguarding is done by the underlying TCP protocol. "MODBUS over TCP" is a variant where a payload is MODBUS RTU data containing a checksum. | "MODBUS TCP" "MODBUS over TCP" | "MODBUS TCP" | ||||||
| Maximum count of registers that are read by one request. | - | 100 | ||||||
| Maximum count of bytes that are required by one request (only in "Byte mode"). | - | 100 | ||||||
| To read the values from addresses that are not configured is not allowed. Description and example: | YES/NO | NO | ||||||
| If this parameter is set to YES, then an extra check is performed when receiving a response to a read request: the length of received data is checked whether it matches the number of registers in a read request:
| YES/NO | NO |
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Independent addressing with the address size of 2 bytes, i.e. addresses from 0 up to 65535 (so-called MODBUS PDU addressing model), is in each address space of given type of register. Some devices work with address space starting with 1 (so-called MODBUS Data Model). In this case, it is necessary to deduct -1 in the address at configuration I/O tags in the D2000 system or change the setting of the parameter Addressing model to the MODBUS data Model.
I/O tag address can be in a basic or extended format (for a variable mode).
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- First character defines a type of I/O tag:
- I - Integer16 (default) - one register is read, signed
- U - Unsigned16 - one register is read, unsigned
- Uu - Unsigned16 - one register is read, unsigned, only upper byte is considered (1st in sequence)
- Ul - Unsigned16 - one register is read, unsigned, only lower byte is considered (2nd in sequence)
- f - Float (4 bytes = 2 registers) - two registers with Address and Address+1 are read and transmitted as big-endian (see Note).
- F - Float (4 bytes = 2 registers) - two registers with Address and Address+1 are read and transmitted as little-endian (so-called Modicon format), (see Note)
- L - Unsigned long (4 bytes = 2 registers) - two registers with Address and Address+1 are read, unsigned, and transmitted as big-endian (see Note)
- Ll - Unsigned long (4 bytes = 2 registers) - two registers with Address and Address+1 are read and transmitted as little-endian, unsigned (see Note)
- S - Signed long (4 bytes = 2 registers) - two registers with Address and Address+1 are read, signed, and transmitted as big-endian (see Note)
- Sl - Signed long (4 bytes = 2 registers) - two registers with Address and Address+1 are read and transmitted as little-endian, signed (see Note)
- B - Byte unsigned, only the upper 8 bits of the register value
- X - Byte unsigned, only the lower 8 bits of the register value.
- sn. - Text string with the length of n characters, one register is one character, n registers with Address up to Address+n-1 are read
- an. - Text string with the length of 2*n characters, one register is two ASCII characters, characters are transmitted in the same order as they appear in the string, n registers with Address up to Address+n-1 are read
- An. - Text string with the length of 2*n characters, one register is two ASCII characters, characters are transmitted in big-endian order (i.e. "1234" is transmitted as "2143"), n registers with Address up to Address+n-1 are read
- Modifier Modifier d indicates that a number is an 8-byte number (4 consecutive registers). It can be used for types L, Ll, S, Sl, F,f, and it is used for configuration of signed/unsigned 8-byte integer as well as an 8-byte float (big-endian <B8>..<B1> and little-endian <B1>..<B8> formats).
Modifier D indicates that a number is an 8-byte number (4 consecutive registers). It can be used for types Ll, Sl, F and it is used for configuration of signed/unsigned 8-byte integer as well as an 8-byte float (little-endian format <B2><B1><B4><B3><B6><B5><B8><B7>).
Note: when using a modifiers d or D, the I/O tag must be of Analog type (Ai), because Integer type (Ci) in D2000 is implemented as a 4-byte variable and overflow might occur. Writing of Integer type (Co) as an 8-byte number is supported. - Modifier Modifier b indicates that figure is coded by BCD. It can be used for I/O tags of I, U, B, L, Ll types.
Modifier Modifier s indicates that a status register (Unsigned16) located on address Address is followed by a big-endian Float value located on address Address+1 .. Address+2. This indicator is used for type f and it is implemented for calorimeter Endress+Hauser RMS621. Following The following table shows the values of the status register and their mapping to D2000 attributes.
Status register D2000 attributes 0 : Invalid value Weak 1 : Measured value valid Valid 2 : Overflow warning
3 : Overflow error
4 : Underflow warning
5 : Underflow error
6 : Saturated steam alarm
7 : Error in differential pressure calculation
8 : Wrong medium for DP calculation
9 : Wrong value range - DP calculation inaccurate
10 : Differential pressure - general error
11 : Range overshoot (Tsat > 350 etc.) on
12 : Change in state of aggregation
26 : Differential pressure --> general error
99 : No measured value is assigned to the register in the setup of the ModBusWeak - Parameter RdFn is a function of the Modbus protocol for a data reading. The following functions are implemented:
- 1 - Read Coils: binary status reading
- 2 - Read Discrete Inputs: binary input reading
- 3 - Read Holding Registers: status register reading (Integer16/Unsigned16 and Float32 - reads two successive registers)
- 4 - Read Input Registers: input register reading (Integer16/Unsigned16 and Float32 - reads two successive registers)
- 0 - A value is not read, it is only written. The function for writing (WrFn) must be set.
- Parameter WrFn is the function of the Modbus protocol for data writing. Following The following functions are implemented:
- 5 - Write Single Coil: binary status writing (default for Read Coils)
- 6 - Write Single Register: status register writing (default for Read Holding Registers)
- 16 - Write Multiple registers: multiple registers writing, it must be used when 2-register type is written (e.g. Float, Unsigned long, etc.).
Note: function can be used to write more than two registers at once if a text string is used. Example:
if we have an I/O tag with address a3.0-16.#8A00 (i.e. text string covering 3 registers, having length of 6 characters) and we write a string '123456', then hexadecimal values 0x3132, 0x3334 and 0x3536 (ASCII code for '1' is 0x31, for '2' is 0x32 etc) will be written to registers 0x8A00, 0x8A01 and 0x8A02. - 22 - Mask Write Register: write affects only the value of the particular bit BitNr of the status register. It is usable only for Do value types with the address parameter BitNr.
- Parameter Parameter d activates the function "delayed write". Sending of the value is delayed until the request to write the value of the object without parameter d comes. All accumulated requests waiting to be written are sent. If the function WrFn is set to "Write Multiple Registers", the values are sent in one packet.
- Parameter Address is a 2-byte address of register (0-65536). See also the protocol parameter Addressing model.
Note: address can be specified as a hexadecimal number using a number sign (#), e.g. #50CE - Parameter BitNr is a number of bit in a word. The values 0-7 are allowed to be used for binary statuses and inputs, values 0-15 are allowed to be used for reading of bit from 16-bit status or input registers.
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3. When values are read from two registers as little-endian the received bytes are analysed in this way (if Little Endian Mode=2143):
Least significant register (ADR address) | Most significant register (ADR+1 address) | ||
MSB | LSB | MSB | LSB |
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- 1.10 - the function Read Coils reads the binary status value with address 10.
- 3.1 - a signed 16-bit number, it is read by the function Read Holding Registers from the address 1 (it can be also in the form I3.1).
- U3.1 - an unsigned 16-bit number without sign that is read by the function Read Holding Registers from address 1.
- I3-6.1000 - signed 16-bit number with sign that is read by the function Read Holding Registers from address 1000 and written by the function Write Single Register (as this function is the default, the address could be also I3.1000).
- S3.321 - a signed 32-bit number with sign, it is read by the function Read Holding Registers from the registers 321 and 322.
- B1.20.0 - a bit that is read by function Read Coils from address 20 as 0-bit in a byte.
- s10.3.123 - a text string, length 10 characters (2 bytes per character), it is read by the function Read Holding Registers from the address 123.
- a5.3.123 - a text string, length 10 characters (1 byte per character), it is read by the function Read Holding Registers from the address 123.
- U0-6.456 - an unsigned 16-bit number, unsigned, is written to the register 456, it is written by Write Single Register, a register reading is not executedperformed.
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- xN indicates the number of bytes that read or write. Valid values for N are 1, 2, 4 (in combination with I, U, F), 6 for T type, and an arbitrary number for C type.
- A letter defines the type of I/O tag. Beside Besides standard I, U, F, B, two extra types have been added:
- C - text string of fixed length (e.g. x10.C3.1001 is a 10-character string on address 1001)
- T - time stamp with length of 6 bytes (ss:mi:hh dd:mm:yy)
- A The meaning of other parameters is in compliance with invariable the standard mode.
See the example of the configuration in the next section.
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- configuration software ROCLINK800
- default login LOI, password 1000
- logging in FloBoss 103: click on DirectConnect (connection through COM1, on the side of FloBoss 103 it is connected to LOI-local interface)
- menu Configure->Modbus->Configuration
set the parameter "Variable Mode" on station in D2000 according to setting "Byte Order":- if "Least Significant Byte first" then "Little endian"
- if "Most Significant Byte first" then "Big endian"
- I/O tags are configured through menu Configure -> Modbus -> Registers on FloBoss 103
- following types are supported (n means 16-bit address):
- Binary input:
- address in D2000: 1.n, e.g. 1.1001, variable of Di/Dout type
- address in FloBoss 103: variable of BIN type
Function: 1
Starting/ending register: n
- Binary output:
- address in D2000: 1.n, e.g. 1.1001, variable of Dout type
- address in FloBoss 103: variable of BIN r/w
Function: 1 (for reading)
Starting/ending register: n
Function: 5 (for reading)
Starting/ending register: n
- Unsigned Int 8 bits input:
- address in D2000: x1.B3.n, e.g. x1.B3.1003, variable of Ci/Co type
- address in FloBoss 103: variable of UINT8 type
Function: 3A or 3B
Starting/ending register: n
- Unsigned Int 8 bits output:
- address in D2000: x1.B3.n, e.g. x1.B3.1003, variable of Co type
- address in FloBoss 103: variable of UINT8 r/w type
Function: 3A or 3B
Starting/ending register: n
Function: 6
Starting/ending register: n
- Unsigned Int 16 bits input:
- address in D2000: x2.U3.n, e.g. x2.U3.1004, variable of Ci/Co type
- address in FloBoss 103: variable of UINT16 type
Function: 3A or 3B
Starting/ending register: n
- Unsigned Int 16 bits output:
- address in D2000: x2.U3.n, e.g. x2.U3.1004, variable of Co type
- address in FloBoss 103: variable of UINT16 r/w type
Function: 3A or 3B
Starting/ending register: n
Function: 6
Starting/ending register: n
- Signed Int 16 bits input:
- address in D2000: x2.I3.n, e.g. x2.I3.1005, variable of Ci/Co type
- address in FloBoss 103: variable INT16 type
Function: 3A or 3B
Starting/ending register: n
- Signed Int 16 bits output:
- address in D2000: x2.I3.n, e.g. x2.I3.1005, variable of Co type
- address in FloBoss 103: variable of INT16 r/w type
Function: 3A or 3B
Starting/ending register: n
Function: 6
Starting/ending register: n
- Unsigned Int 32 bits input:
- address in D2000: x4.U3.n, e.g. x4.U3.1006, variable of Ci/Co type
- address in FloBoss 103: variable of UINT32 type
Function: 3A or 3B
Starting/ending register: n
- Unsigned Int 32 bits output:
- address in D2000: x4.U3.n, e.g. x4.U3.1006, variable of Co type
- address in FloBoss 103: variable of UINT32 r/w type
Function: 3A or 3B
Starting/ending register: n
Function: 6
Starting/ending register: n
- Float 32 bits input:
- address in D2000: x4.F3.n, e.g. x4.F3.1008, variable of Ai/Ao type
- address in FloBoss 103: variable of FL type
Function: 3A or 3B
Starting/ending register: n
- Float 32 bits output:
- address in D2000: x4.F3.n, e.g. x4.F3.1008, variable of Co type
- address in FloBoss 103: variable of FL r/w type
Function: 3A or 3B
Starting/ending register: n
Function: 6
Starting/ending register: n
- String (N bytes) input:
- address in D2000: x1N.C3.n, e.g. x10.C3.1010, variable of TxtI/TxtO type
- address in FloBoss 103: variable of ACm(AC10,AC12,AC20,AC30,AC40) type
Function: 3A or 3B
Starting/ending register: n
- String (N bytes) output:
- address in D2000: xN.C3.n, e.g. x10.C3.1010, variable of Co type
- address in FloBoss 103: variable of ACN r/w type (AC10,AC12,AC20,AC30,AC40)
Function: 3A or 3B
Starting/ending register: n
Function: 6
Starting/ending register: n
- Time and date 6 bytes input:
- address in D2000: x6.T3.n, e.g. x6.T3.1010, variable of TiA/TxtI type
- address in FloBoss 103: variable of DT6 type
Function: 3A or 3B
Starting/ending register: n - Note 1: FloBoss 103 supports local and monotonous time - that is why the configuration of station in D2000 must correspond to configuration of FloBoss.
- Note 2: It is possible to set time and date but it requires to configure extra the I/O tags for a second, minute, hour, day, month, and year as Unsigned Int 8 bits and after that to write into them.
- Binary input:
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on Honeywell controllers
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The basic parameters and current data of these controllers are not normally read by means of functions 0x01 up to 0x04. There It is necessary to use the function 0x14/0x15 Read/write configuration reference data. These controllers use "big-endian" byte order. Therefore, for proper functionality, it is not necessary to modify parameters that changes change byte mode and endianness.
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