The MODBUS^® protocol represents an industrial communication system distributed and developed by Gould-Modicon to integrate PLC’s, computers, terminals, inverter and other devices. MODBUS is a Master/Slave communication protocol where only one device can be Master and monitors all activities of the serial line or TCPIP. As for the serial line can be connected up to a maximum of 247 slave along the same lines. Each device is assigned an address that distinguishes it from all other connected devices.
The MODBUS device lets you choose which serial port use for connection. The features s of data transmission (number of device, baud rate, parity, stop bits) and the transmission mode must be selected on each station and cannot be changed during the operation.
With using a serial line, there are two modes of transmission used in the Modbus Protocol. Both ways allow the same communication skills. The mode is selected by the master and must be unique for all devices connected to the network. The modes are:

• ASCII (American Standard Code for Information Interchange)
• RTU, (Remote Terminal Unit.)

This manual is divided into two parts:
Part I - Operation as master
Part II - Operation as slave.

The modbus communication protocol standard defines 4 types of Exchange data:

• INPUT STATUS = Digital Inputs
• COIL STATUS = UDigital Outputs
• INPUT REGISTER = Analog Inputs
• HOLDING REGISTER. = Analog Outputs

Throughout the manual you have to take into account existing conventions.

Declaration of the used device (internal device): device name assigned, MODBUS, slot location and number of the device.

INTDEVICE
...
<device_name>      MODBUS    TCamp    channel
...

Where:

To declare the hardware used in the “BUS” section of the configuration unit you will have to refer to the firmware of the hardware itself.

Example

INTDEVICE
modbus             MODBUS     0002    1

NOTE 1: the “ iword1 ” is the most significant word of the “ ilong1 ” (long = double word), the “iword3” is the most significant word of the “ ilong2 ”, …
NOTE 2: the “ st_ibit0 ” parameter less significant bit (with weight 0) of the “ iword1 ”, while the “ st_ibit15 ” bit is the most significant (with weight 15) of the “ iword1 ”.

NOTE 1: the “ oword1 ” is the most significant word of the “ olong1 ” (long = double word), the “oword3” is the most significant word of the “ olong2 ”, …
NOTE 2: the “ st_obit0 ” parameter is the less significant bit (with weight 0) of the “ oword1 ”, while the “ st_obit15 ” bit is the most significant (with weight 15) of the “ oword1 ”.

The MODBUS device can use a serial port or TCPIP to communicate in master mode (parameter mode = 0). Allows (via parameters, states and commands) all instruments to be able to communicate with any equipment utilizing Modbus.
The device provides a data exchange area where the QCL can write or read values shared with the slaves on the network. This area is represented by a list of parameters of the device divided into two groups to differentiate the type of access of the data by the device. The first section is identified as INPUT the second as OUTPUT. The INPUT section, for master operation, is the storage area of reads data. It is used by all reader functions (parameter type = 1, 2, 3 o 4). The OUTPUT section, in the master operation, is the area of data storage that the master should transfer to the slaves. It is used by all writing functions (parameter type = 5, 6, 15 o 16). To facilitate the exchange of data between devices, the structure of the Exchange area includes data types commonly used in QCL namely WORD, LONG and FLAG. The “BYTE” type does not appear because the modbus usually uses the word size for each address registers. The modbus protocol selects data based on the number of access log register, while the QCL selects based on the parameter symbol, you create a reference table in which each QCL symbol find the corresponding number in the register of access in Modbus protocol. To obtain greater flexibility for addressing, the same area of Exchange data can be manipulated by the QCL with different dimension parameterized. All the symbols that appear in the same row of the table refer to the same memory locations.

The data input or coil type have in the modbus Protocol a bit size. To store this information in the table of data exchange is defined as follows mode: each register (and then every word parameter of the device) represents 16 elements that are numbered from left to right. For the Scriptures or multiple readings when bits read are higher than those contained in the register the operation continues in the next register.
The st_ibit0… and st_obit1… states are useful in order to facilitate access to information bit, only in the first table log.

The master mode is set with the mode parameter = 0. The card generates modbus messages only on QCL ordering and does not automatically. To “format” the modbus message string there are a number of parameters.
Using the two commands SEND or SENDSYC you send the read or write request to the slave, a number of States allow an audit on the operation being executed. We see in detail:

type = request type that you want to process (reading or writing word or bit).
idcard = address of the slave drive to which you want to send the request.
addr = the index from which to start reading or at which to start writing in the slave.
tabreg = for read operations (type = 1, 2, 3, 4), This parameter indicates the position in the “table of data read” where will store the read data on the slave. For write operations (type = 5, 6, 15, 16), this parameter indicates the position in the “table of data to be written” where is the data to be written on the slave. Are accepted values are between 1 and 512 for values of type parameter = 1, 2, 5, 15 (writing and reading of bits), while for type value = 3, 4, 6, 16 (writing and reading of word) the expected values are between 1 and 32.
num = number of values that are read or write (if the request type so provides). Are accepted values are between 1 and 128 for values of type parameter = 1, 2, (reading of bits), while for type value = 3, 4, 16 (multiple word reading and writing) the accepted value are between 1 and 32.

SEND sends the request message to the slave.
SENDSYC sends the request message to a QEM slave of MODBUS type and reports the operation concluded (st_sended) only when the slave executes the RECEIVED command.

When ended the message send operation, the status st_sended variable is set to 1. If you used the SEND command the state is set to 1 when the master receive the confirmation of the message being sent. If you have used the SENDSYC command in the master then this status will be set to 1 when the slave QEM will execute the RECEIVED command. In case of error, This status is still in set to 1 (After the toutsyc time) but the err parameter indicates the cause of the error (see the description of this parameter for details).
The SENDSYC coomand it becomes necessary when you want to synchronize master data packet writing by reading the same data from the slave (can be used when both master and slave are Qmove).

Bit read function. You want to read the bits of a slave (idcard). Sets the parameter type = 1.
You must set addr to indicate the address of the bit in the slave from which to start reading. The num parameter indicates the number of bits that are read. You must to set tabreg to indicate the index of the bit in the “data read table” the master from which you want to be written the read bits. The raedings value will be saved in the “data read table”. It is recommended to always meet the following two conditions:
(addr + num - 1) ⇐ 512 e (tabreg + num - 1) ⇐ 512 otherwise the request will fail (reporting by wcmd).

Bit read function. To read the bits of a slave (idcard). The function is equal to the “Read Coil”. Sets the parameter type = 2.
The meaning of the two functions is distinguished at the level of MODBUS protocol. Some slave can make available different memory areas depending if the bits are Coil or Input. In the case of slave Qmove the two requests have the same effect.

Word read function. For reading the word of the slave (idcard). Sets the parameter type = 3.
You must to set addr to indicate the address of the word in the slave from which to start reading. The num parameter indicates the number of word to be read. You must set tabreg to indicate the index of the word in the “read data table” of the master from which you want are writes the read words. The read values will be saved in the “read data table”. It is recommended to always meet the following two conditions:
(addr + num - 1) ⇐ 32 e (tabreg + num - 1) ⇐ 32 otherwise the request will fail (reporting by wcmd).

Word read function. For reading the bit of the slave (idcard). The function is equal to the “Read Holding Register”. sets the parameter type = 4.
The meaning of the two functions is distinguished at the level of MODBUS protocol. Some slave can make available different memory areas depending if the read word are Holding or Input. In the case of slave Qmove the two requests have the same effect.

Bit write function. For writing (force) the bit of the slave (idcard). Sets the parameter type = 5.
You must set addr to indicate the address of the bit in the slave that you want to write. You must set tabreg to indicate the index of the bit in the “write data table” that contains the value to be written.

Word write function. For write (force) the word of a slave (idcard). Sets the parameter type = 6.
You must set addr to indicate the address of the word in the slave that you intend to write. You must set tabreg to indicate the index of the word in the “data write table” that contains the value to be written.

Multiples bit write function. For write (force) the bit of a slave (idcard). Sets the parameter type = 15.
You must set addr to indicate the address of the bit in the slave that you intend to write. You must set in num the number of bits to write. You must set tabreg to indicate the bit index of the “data write table” from which to begin the values to be written. It is recommended to always meet the following two conditions:
(addr + num - 1) ⇐ 512 e (tabreg + num - 1) ⇐ 512 otherwise the request will fail (reporting by wcmd).

Multiples word write function. For write (forzare) the word of a slave (idcard). Sets the parameter type = 16.
You must set addr to indicate the address of the word in the slave that you intend to write. You must set in num the number of word to write. You must set tabreg to indicate the index of the word in the “dat write table” from which to begin the values to be written. It is recommended to always meet the following two conditions:
(addr + num - 1) ⇐ 32 e (tabreg + num - 1) ⇐ 32 otherwise the request will fail (reporting by wcmd).

1) Modbus settings and opening of serial communication

modbus.mode = 0                             ; modbus master
modbus.prot = 1                             ; RTU
modbus.brate = 57600                        ; baudrate
modbus.stopb = 1                            ; stop bits
modbus.par = 0                              ; parity
modbus.tout = 100                           ; timeout
 
modbus.OPENCOM
tm_opencom = 200                            ; timeout for OPENCOM command
WAIT modbus.st_opencom OR tm_opencom
IF NOT modbus.st_opencom
    OpenComError = 1                        ; com not opened
ENDIF

2) Impostazioni modbus e apertura del canale di comunicazione di tipo TCPIP

modbus.mode = 0                             ; modbus master
modbus.prot = 2                             ; TCPIP
modbus.tout = 100                           ; timeout
 
tcpip_port= 502                             ; number of tcpip port (default 502)
modbus.stopb = (tcpip_port ANDB &H0000FF00) / 256
modbus.par = tcpip_port ANDB &H000000FF
 
modbus.OPENCOM
tm_opencom = 500                            ; waiting time to have a correct response
WAIT tm_opencom
IF NOT modbus.st_opencom
    OpenComError = 1                        ; com not opened
ENDIF

3) Reading the registry input nr.7 of the slave id 67

modbus.idcard = 67
modbus.addr = 7
modbus.tabreg = 7
modbus.num = 1
modbus.type = 4
modbus.SEND
WAIT modbus.st_sended
IF (modbus.err)
    CALL ErrorModbus
ENDIF
slSpeed = modbus.iword7

4) Reading of the holding register from nr.600 to nr.606 of the slave id 8
The area of QCL data exchange does not support the address 600, you use the tabreg parameter to save the data read at 10 address

modbus.idcard = 8
modbus.addr = 600
modbus.num = 6
modbus.tabreg = 10
modbus.type = 3
modbus.SEND
WAIT modbus.st_sended
IF (modbus.err)
    CALL ErrorModbus
ENDIF
 
swTemp1 = modbus.iword10
slSpeed = modbus.ilong6
slPosiz = modbus.ilong7
swTemp1 = modbus.iword15

The Broadcast is a special message that is sent by the Master and is received simultaneously from all connected slaves. The broadcast function (idcard = 0) is supported only in master mode and if you use a message with type = 5, 6, 15 and 16 (write only). In this mode the st_sended state is activated once ended the transmission and not on receipt of confirmation by the slave. There isn't answer on the slaves to such messages. You cannot use the SENDSYC command.

When the card works in master mode allows, with specila command, tell if the slave connected is a QEM. If so also determines the pattern of slave connected. This allows a diagnostic on the correct network configuration. You cannot extend this control to all types of existing slaves because the protocol does not provide a standard way of slave recognition.
The READSTYPE command executed after selecting the slave (through idcard parameter) send a nr.17 modbus request to the slave for recognition. The slave will responds with a default value and can be read in the stype parameter of the master. If the slave is not produced by QEM, the parameter will be –1 value to indicate that the slave is connected but you cannot identify it.
For the MODBUS device the ID slave is different depending on the slave QEM used. For encoding of the slaves see the slave Firmware used.

Example of slave identification nr.12:

modbus:idcard = 12
modbus.READSTYPE
WAIT modbus.st_sended
IF (modbus.err)
    sbConfig = 3             ; error: slave 12 not connected
ELSE
    IF (modbus.stype EQ 1)   ; Board CAM-AG-98
        sbConfig = 1         ; configuration OK
    ELSE
        sbConfig = 2         ; error in network configuration
    ENDIF
ENDIF

The modbus standard communication protocol defines 4 types of Exchange data:

• INPUT STATUS,
• COIL STATUS,
• INPUT REGISTER,
• HOLDING REGISTER.

These 4 types treat signals as Digital Inputs, Digital Outputs, Analog Inputs, and Analog Outputs. The values of the registers (INPUT REGISTERS and HOLDING REGISTERS), are defined as values in 16 bit, each with a unique address, (example INPUT REGISTER #1, INPUT REGISTER #2, INPUT REGISTER #3, ecc.).
To allow support for datatypes larger than 16 bit, has been designed an extension to the protocol to treat long 32 bit dimension values. Implementing this feature preserves the formatting of the message standard modbus it uses the contents of two consecutive addresses to represent a 32 bit value. When this extension is enabled (wider = 1), depending on the address used the slave responds with a 16-bit or 32-bit value for each log request. If the address is greater than 5000 will be returned a 32-bit value, if under the Protocol remains unchanged with response to 16 bits.

The parameter name, condition or command is taken back to the left side of the table.

R
Indicates if the parameter or state is retentive (upon initialization of the device maintains the previously defined state), or the state assumes upon initialization of the device.
If the device does not need to initialize the “R” field indicates the value that the parameter or state take at the at power-up card.
R = Retentive
0 = Upon initialization of the device the value is forced to zero.
1 = Upon initialization of the device the value is forced to one.
- = Upon initialization of the device is presented significant value.

D
Indicates the size of the parameter.
F = Flag
B = Byte
W = Word
L = Long
S = Single Float

Describes all the conditions necessary for the parameter so that the parameter is considered correct or because the command is accepted.
In some cases, limit values are specified for the acceptance of the parameter: if any values outside the limits set are introduced, the data is however accepted; therefore appropriate controls of the application must be provided to ensure the proper functioning.
To execute a command, all conditions must be met; otherwise the command does not execute.

A
Indicates the access mode.
R = Read.
W = Write.
RW = Read / Write.

The ability to communicate with the TCPIP protocol It was developed at a later time than the birth of the MODBUS device. For this reason the IP address and port setting is achieved using some parameters that have a different meaning.

To configure the TCPIP port number You must go and write about the stopb and par parameters. Respectively :

• stopb = tcpip_port / &H00000100
• par = tcpip_port ANDB &H000000FF

To set the TCPIP slave to which you want to execute the request you must go to write on thebrate parameter .
An IP address can be expressed as TcpAddr3.TcpAddr2.TcpAddr1.TcpAddr0 (for example 192.168.0.1).

• brate = (TcpAddr3 * &H01000000) + (TcpAddr2 * &H00010000) + (TcpAddr1 * &H00000100) + TcpAddr0

The available commands to manage the device are listed below in descending order of priority.
The device executes all commands received within the same sampling time starting from the one with the highest priority.
For example if the device receives the same sampling time CLOSECOM and OPENCOM commands, first run the OPENCOM command and then to CLOSECOM leaving therefore the communication port closed.

Slave mode is set with the mode = 1 or mode = 2 parameter. You must to introduce in the parameters the slave ID code through the idcard parameter.

Modbus settings and opening channel of serial communication

modbus.mode = 1                             ; modbus slave
modbus.prot = 1                             ; RTU
modbus.brate = 57600                        ; baudrate
modbus.stopb = 1                            ; stop bits
modbus.par = 0                              ; parity
modbus.idcard = 1                           ; slave id
 
modbus.OPENCOM
tm_opencom = 100                            ; timeout for OPENCOM command
WAIT modbus.st_opencom OR tm_opencom
IF NOT modbus.st_opencom
    OpenComError = 1                        ; com not opened
ENDIF

Modbus settings and open of the communication channel of TCPIP type

modbus.mode = 1                             ; modbus slave
modbus.prot = 2                             ; TCPIP
 
tcpip_port= 502                             ; number of tcpip port (default 502)
modbus.stopb = (tcpip_port ANDB &H0000FF00) / 256
modbus.par = tcpip_port ANDB &H000000FF
 
modbus.OPENCOM
tm_opencom = 100                            ; waiting time to have a correct response
WAIT (modbus.st_opencom OR timerOpencom)
IF NOT modbus.st_opencom
    OpenComError = 1                        ; com not opened
ENDIF

The operations that should execute the QCL are essentially two:

• update the parameters owordNN, olongNN type (which will then be read from the master)
• process the parameters iwordNN, ilongNN type (which will then written by the master)

To update the owordNN parameters type the QCL must write values in the parameters then send the VALIDATE command. The use of the command is necessary to make available on the readings of the master the new data at the same time, so that they can be read only part of updated parameters. So assigning a value to a device parameter DOES NOT MEAN that it is immediately available for the master readings. Will only be available after the VALIDATE command.

Example

modbus.olong1 = anpos.speed
modbus.oword1 = npezzi
modbus.oword2 = npezzitot
modbus.oword3 = anpos.dir
modbus.olong2 = anpos.posit
modbus.VALIDATE

To process the iwordNN parameters type, instead,the QCL must wait for the st_msgrx state is activated. This means that a write message was sent by the master. For the read message no signal reportedly to QCL parameters. The QCL then must take the values from the data exchange and at the end needs to send the RECEIVED command, only then the st_msgrx state is disabled.

Example

WAIT modbus.st_msgrx
anpos.speed = modbus.ilong1
anpos:posit = modbus.ilong2
npezzi = modbus.iword1
RECEIVED modbus

There is no control to prevent when reading iwordNN parameters the master incorrectly execute another writing, before the project code present in the slave to finish the process.
Also the code for handling the modbus device in the application it is recommended that it is collected in a single task in order not to create simultaneous accesses to the device that could generate invalid conditions.

All read requests that arrive from the master MODBUS refer to the owordNN type data by accessing to the same data area. The slave provides the values that the master will read in the owordNN parameters type.
All write requests arriving from the MODBUS master refer to the iwordNN type data aby accessing to the same data area. The slave provides the iwordNN parameters where the master will write data.

The parameter name, condition or command is shown at the left of the table.

R
Indicates if the parameter or state is retentive (upon initialization of the device maintains the previously defined state), or the state assumes upon initialization of the device.
If the device does not need to initialize the “R” field indicates the value that the parameter or accept to the power up of the card.
R = Retentive
0 = Upon initialization of the device the value is forced to zero.
1 = Upon initialization of the device the value is forced to one.
- = Upon initialization of the device is presented significant value.

D
Indicates the size of the parameter.
F = Flag
B = Byte
W = Word
L = Long
S = Single Float

Describes all the conditions necessary so that the parameter is considered correct or because the command is accepted.
In some cases, limit values are specified for the acceptance of the parameter: if there are any values outside the limits set, the data is however accepted; therefore appropriate controls of the application must be provided to ensure the proper functioning.
To execute a command, all conditions must be met; otherwise the command is not executed.

A
Indicates the access mode.
R = Read.
W = Write.
RW = Read / Write.

The available commands to manage the device are listed below in descending order of priority.
The device executes all commands received within the same sampling time starting from the one with the highest priority.
For example if the device receives the same sampling time CLOSECOM and OPENCOM commands, first run the OPENCOM command and than to CLOSECOM leaving therefore the communication port closed.

The first thing to note for migration is the fact that the MODBUS01 device is external, while the MODBUS is internal. This implies that the device declaration must be done in “INTDEVICE” section in the configuration unit of the project. In addition, this entails choosing, when defining the MODBUS device, of the sampling time. The value of the sample time that keeps the performance of communication between the two devices is 5 ms. Being defined, you must select the serial port to be committed.
The MODBUS device increased the number of exchange variables (from 16 word to 32 word) but this does not affect the operation for settings that use the maximum 16 word How are those designed for the MODBUS01 device.
The MODBUS device has restricted the “num” variable to 128, while the MODBUS01 device the limit is 256. This was necessary to allow an optimization of sampling time. The decision was taken in view of the fact that those values were used only for Coils managing, but that was logic leaking more than read/write 128 consecutive coils.
The MODBUS device allows you to control (using 2 new commands) communication serial's commitment on the part of the device. This new functionality is interesting in the event that other devices have been declared in a project Qview that can use the same serial.
If an application was written for the MODBUS01 device you must add the OPENCOM command (executed only once) as shown in the following example.

; setting communication parameters
modbus.mode = 0
modbus.brate = 38400
...
modbus.OPENCOM
WAIT modbus.st_opencom
 
modbus.idcard = 8
modbus.addr = 600
modbus.num = 6
modbus.tabreg = 10
modbus.type = 3
modbus.SEND
WAIT modbus.st_sended
IF (modbus.err)
    CALL ErrorModbus
ENDIF