go modbus

Fault-tolerant, fail-fast implementation of Modbus protocol in Go.

Supported functions

Bit access:

• Read Discrete Inputs
• Read Coils
• Write Single Coil
• Write Multiple Coils

16-bit access:

• Read Input Registers
• Read Holding Registers
• Write Single Register
• Write Multiple Registers
• Read/Write Multiple Registers
• Mask Write Register
• Read FIFO Queue

Supported formats

• TCP
• Serial (RTU, ASCII)
• UDP

Usage

Basic usage:

// Modbus TCP
client := modbus.TCPClient("localhost:502")
// Read input register 9
results, err := client.ReadInputRegisters(8, 1)

// Modbus RTU/ASCII
// Default configuration is 19200, 8, 1, even
client = modbus.RTUClient("/dev/ttyS0")
results, err = client.ReadCoils(2, 1)

Advanced usage:

// Modbus TCP
handler := modbus.NewTCPClientHandler("localhost:502")
handler.Timeout = 10 * time.Second
handler.SlaveID = 0xFF
handler.Logger = log.New(os.Stdout, "test: ", log.LstdFlags)
// Connect manually so that multiple requests are handled in one connection session
err := handler.Connect()
defer handler.Close()

client := modbus.NewClient(handler)
results, err := client.ReadDiscreteInputs(15, 2)
results, err = client.WriteMultipleRegisters(1, 2, []byte{0, 3, 0, 4})
results, err = client.WriteMultipleCoils(5, 10, []byte{4, 3})

// Modbus RTU/ASCII
handler := modbus.NewRTUClientHandler("/dev/ttyUSB0")
handler.BaudRate = 115200
handler.DataBits = 8
handler.Parity = "N"
handler.StopBits = 1
handler.SlaveID = 1
handler.Timeout = 5 * time.Second

err := handler.Connect()
defer handler.Close()

client := modbus.NewClient(handler)
results, err := client.ReadDiscreteInputs(15, 2)

Modbus-CLI

We offer a CLI tool to read/write registers.

Usage

For simplicity, the following examples are all using Modbus TCP. For Modbus RTU, replace the address field and use the rtu- arguments in order to use different baudrates, databits, etc.

./modbus-cli -address=rtu:///dev/ttyUSB0 -rtu-baudrate=57600 -rtu-stopbits=2 -rtu-parity=N -rtu-databits=8 ...

For Modbus UDP, replace the address field with a UDP address.

./modbus-cli --address=udp://127.0.0.1:502 ...

Reading Registers

Read 1 register and get raw result

./modbus-cli -address=tcp://127.0.0.1:502 -quantity=1 -type-parse=raw -register=42

Read 1 register and decode result as uint16

./modbus-cli -address=tcp://127.0.0.1:502 -quantity=1 -type-parse=uint16 -register=42

Read 1 register and get all possible decoded results

./modbus-cli -address=tcp://127.0.0.1:502 -quantity=1 -type-parse=all -register=42

Read 2 registers and decode result as uint32

./modbus-cli -address=tcp://127.0.0.1:502 -quantity=2 -type-parse=uint32 -register=42

Read 2 registers and get all possible decoded results

./modbus-cli -address=tcp://127.0.0.1:502 -quantity=2 -type-parse=all -register=42

Reading multiple registers is only possible in the raw format

./modbus-cli -address=tcp://127.0.0.1:502 -quantity=16 -type-parse=raw -register=42

Writing Registers

Write 1 register

./modbus-cli -address=tcp://127.0.0.1:502 -fn-code=0x06 -type-exec=uint16 -register=42 -write-value=7

Write 2 registers

./modbus-cli -address=tcp://127.0.0.1:502 -fn-code=0x10 -type-exec=uint32 -register=42 -write-value=7

Release

To release the Modbus-CLI tool, run either make release if you have installed goreleaser or make ci_release. The generated files can be found in the directory in the dist directory.

Take the .tar.gz and .zip files and create a new GitHub release.

References

• Modbus Specifications and Implementation Guides