Modbus RTU

Modbus RTU is a version of the Modbus protocol that is based on serial communication. Unlike the Modbus TCP protocol, Modbus RTU is typically used to connect sensors, actuators, and other control devices on a factory production line. It is a fast, reliable, and flexible serial communication protocol that provides reliable data transmission and control functions.

The Modbus RTU protocol uses binary encoding and can transmit data over RS-232, RS-485, or other serial communication media. The Modbus RTU plugin for Neuron adds an implementation based on Ethernet TCP and enables remote device data acquisition and control through a DTU device.

Parameters

ParameterDescription
Physical LinkSelects the communication medium, either serial or Ethernet.
Connection TimeoutThe time the system waits for a device to respond to a command.
Send IntervalThe waiting time between sending each read/write command. Some serial devices may discard certain commands if they receive consecutive commands in a short period of time.
Serial DeviceThe path to the serial device when using a serial connection, e.g., /dev/ttyS0 in Linux systems.
Stop BitsSerial connection parameter.
ParitySerial connection parameter.
Baud RateSerial connection parameter.
Data BitsSerial connection parameter.
Connection ModeWhen selecting Ethernet TCP connection, you can choose Neuron as the TCP client or server.
IP AddressThe IP address of the device when using TCP connection with Neuron as the client, or the IP address of Neuron when using TCP connection with Neuron as the server. The default value is 0.0.0.0.
PortThe port number of the device when using TCP connection with Neuron as the client, or the port number of Neuron when using TCP connection with Neuron as the server.
Maximum Retry TimesThe maximum number of retries after a failed attempt to send a read command.
Retry IntervalResend reading instruction interval(ms) after a failed attempt to send a read command.
Transport ModeTCP transfer or UDP transfer

Data types

  • INT16
  • UINT16
  • INT32
  • UINT32
  • INT64
  • UINT64
  • FLOAT
  • DOUBLE
  • BIT
  • STRING

Address format

SLAVE!ADDRESS[.BIT][#ENDIAN][.LEN[H][L][D][E]]

SLAVE

Required, Slave is the slave address or site number.

ADDRESS

Required, Address is the register address.The Modbus protocol has four areas, each area has a maximum of 65536 registers, and the address range of each area is shown in the table below. It should be noted that the storage area as large as 65536 is generally not required in practical applications. Generally, PLC manufacturers generally use an address range within 10000. Please pay attention to fill in the correct point address according to the area and function code of the device.

AreaAddress RangeAttributeRegister SizeFunction CodeData Type
Coil000001 ~ 065536Read/Write1Bit0x01,0x05,0x0fBIT
Input100001 ~ 165536Read/Write1Bit0x02BIT
Input Register300001 ~ 365536Read/Write16Bit,2Byte0x04BIT,INT16,UINT16,INT32,UINT32,INT64,UINT64,FLOAT,DOUBLE,STRING
Hold Register400001 ~ 465536Read/Write16Bit,2Byte0x03,0x06,0x10BIT,INT16,UINT16,INT32,UINT32,INT64,UINT64,FLOAT,DOUBLE,STRING

TIP

Some device specification documents may use function codes and register addresses to describe commands. Since register address numbers start at 0, the register address range for each area is 0 to 65535. Neuron uses a PLC configuration address specification, so the addresses configured in Neuron start from 1.

The conversion rule for the configuration address specification is as follows: determine the highest digit of the address based on the function code, and add 1 to the register address to obtain the address used in Neuron.

For example, if the function code is 0x03 and the register address is 0, the address used in Neuron is 400001. If the function code is 0x02 and the register address is 5, the address used in Neuron is 100006.

.BIT

Optional, specify a specific bit in a registe

AddressData TypeDescription
1!300004.0bitRefers to station 1, input area, address 300004, bit 0
1!400010.4bitRefers to station 1, hold register area, address 400010, bit 4
2!400001.15bitRefers to station 2, hold register area, address 400001, bit 15

#ENDIAN

Optional, byte order, applicable to data types int16/uint16/int32/uint32/float, see the table below for details.

SymbolByte OrderSupported Data TypesNote
#B2,1int16/uint16
#L1,2int16/uint16Default byte order if not specified
#LL1,2,3,4int32/uint32/floatDefault byte order if not specified
#LB2,1,4,3int32/uint32/float
#BB3,4,1,2int32/uint32/float
#BL4,3,2,1int32/uint32/float

.LEN[H][L][D][E]

When the data type is STRING, .LEN is a required field, indicating the number of bytes the string occupies. Each register contains four storage methods: H, L, D, and E, as shown in the table below.

SymbolDescription
HOne register stores two bytes, with the high byte first
LOne register stores two bytes, with the low byte first
DOne register stores one byte, and it is stored in the low byte
EOne register stores one byte, and it is stored in the high byte

Examples

AddressData TypeDescription
1!300004int16Refers to station 1, input area, address 300004, byte order #L
1!300004#Bint16Refers to station 1, input area, address 300004, byte order #B
1!300004#Luint16Refers to station 1, input area, address 300004, byte order #L
1!400004int16Refers to station 1, hold register area, address 400004, byte order #L
1!400004#Lint16Refers to station 1, hold register area, address 400004, byte order #L
1!400004#Buint16Refers to station 1, hold register area, address 400004, byte order #B
1!300004int32Refers to station 1, input area, address 300004, byte order #LL
1!300004#BBuint32Refers to station 1, input area, address 300004, byte order #BB
1!300004#LBuint32Refers to station 1, input area, address 300004, byte order #LB
1!300004#BLfloatRefers to station 1, input area, address 300004, byte order #BL
1!300004#LLint32Refers to station 1, input area, address 300004, byte order #LL
1!400004int32Refers to station 1, hold register area, address 400004, byte order #LL
1!400004#LBuint32Refers to station 1, hold register area, address 400004, byte order #LB
1!400004#BBuint32Refers to station 1, hold register area, address 400004, byte order #BB
1!400004#LLint32Refers to station 1, hold register area, address 400004, byte order #LL
1!400004#BLfloatRefers to station 1, hold register area, address 400004, byte order #BL
1!300001.10StringRefers to station 1, input area, address 300001, character length 10, byte order L, which occupies addresses 300001 to 300005
1!300001.10HStringRefers to station 1, input area, address 300001, character length 10, byte order H, which occupies addresses 300001 to 300005
1!300001.10LStringRefers to station 1, input area, address 300001, character length 10, byte order L, which occupies addresses 300001 to 300005
1!400001.10StringRefers to station 1, hold register area, address 400001, character length 10, byte order L, which occupies addresses 400001 to 400005
1!400001.10HStringRefers to station 1, hold register area, address 400001, character length 10, byte order H, which occupies addresses 400001 to 400005
1!400001.10LStringRefers to station 1, hold register area, address 400001, character length 10, byte order L, which occupies addresses 400001 to 400005
1!400001.10DStringRefers to station 1, hold register area, address 300001, character length 10, byte order D, which occupies addresses 400001 to 400005
1!400001.10EStringRefers to station 1, hold register area, address 300001, character length 10, byte order E, which occupies addresses 400001 to 400005