Example description

1. Introduction

This example provides functional demonstration of RTU / TCP master and slave.

Using cmake under WSL or Linux, you can directly compile all examples and run the test program on your computer.

Directory Structure:

Name	Description
common	public source code
figures	materials
rtu_master	RTU master example
tcp_master	TCP master example
slave	RTU + TCP slave example
rtu_p2p	RTU peer-to-peer transfer file
rtu_broadcast	RTU broadcast transmission file (sticky packet processing example)

2. Use

The tools you need to prepare are as follows:

Virtual serial port software
Modbus Poll
Modbus Slave

Type cmake -B build 、 cmake --build build on the command line.

2.1. Host

RTU (rtu_master)
- Use virtual serial port software to virtualize a pair of serial ports
- Open Modbus Slave and set as shown below
- Modbus Slave connection, set as shown below
- Enter the build/bin directory, ./RtuMaster /dev/ttySX to run the RTU host example, ttySX is the other of a pair of virtual serial ports
TCP (tcp_master)
- Open Modbus Slave, SetUp settings are consistent with RTU
- Modbus Slave connection, set as shown below
- Enter the build/bin directory, ./TcpMaster 127.0.0.1 502 and run the TCP host example

2.2. Slave machine

This example (slave) provides both RTU and TCP slave function demonstrations, controlling the same memory. TCP can connect to a maximum of 5 clients. Each client has a no-data timeout of 10s and will be automatically disconnected after 10s.
The example supports all function codes (except function code 0x07).
bit, input_bit, register, input_register registers are defined separately for each file.
Use agile_modbus_slave_util_callback.
Register address field:

| Register | Address range | | --- | --- | | Coil register | 0x041A ~ 0x0423 (1050 ~ 1059) | | Discrete input register | 0x041A ~ 0x0423 (1050 ~ 1059) | | Holding register | 0xFFF6 ~ 0xFFFF (65526 ~ 65535) | | Input register | 0xFFF6 ~ 0xFFFF (65526 ~ 65535) |

Note: Reading and writing other address registers can be successful, but the values are all 0.

use:

Use virtual serial port software to virtualize a pair of serial ports

Enter the build/bin directory, ./ModbusSlave /dev/ttyS2 1025 to run the example

/dev/ttySX: One of the virtual serial ports

1025: Listening port number. If you do not have root permissions, the port number must be greater than 1024

Open Modbus Poll and set and connect RTU as shown below

Open 5 Modbus Poll, set the same as RTU, and connect as shown below

Effect demonstration

Timeout disconnect demonstration

Close the poll interface of Modbus Poll and look at the console print to see the close message.

2.3. RTU transmission file

Use 0x50 as the special function code for transferring files.

File data is transferred in packets, with a maximum size of 1024 bytes per packet.

Data field protocol definition:

Host request

| command | number of bytes | data | | ---- | ---- | ---- | | 2 Bytes | 2 Bytes | N Bytes |

Order:

| Command | Description | Data | | ---- | ---- | ---- | | 0x0001 | Start sending | File size (4 Bytes) + file name (string) | | 0x0002 | Transmission data | Flag (1 Byte) + file data |

Logo:

| Status | Description | | ---- | ---- | | 0x00 | The last packet of data | | 0x01 | Not the last packet of data |

Slave response

| Command | Status | | ---- | ---- | | 2 Bytes | 1 Byte |

state:

| Status | Description | | ---- | ---- | | 0x00 | Failure | | 0x01 | Success |

Use virtual serial port software to virtualize 3 serial ports to form a serial port group

Here I use the MX virtual serial port

2.3.1. Point-to-point transmission

Enter the build/bin directory and open Linux Shell. The demonstration effect is as follows

Notice:

The transferred files must be general files. Executable files, directories, etc. are not supported.
The file path must be the path in Linux environment
After the slave receives the data, the file name is modified (slave address_original file name) and written in the current directory.

2.3.2. Broadcast transmission

This example mainly demonstrates the use of frame_length in agile_modbus_slave_handle.

In broadcast_master, use broadcast address 0 and send data packets every 5ms. At the same time, 100 bytes of dirty data are sent after each packet of data.


int send_len = agile_modbus_serialize_raw_request(ctx, raw_req, raw_req_len);
serial_send(_fd, ctx->send_buf, send_len);

//dirty data
serial_send(_fd, _dirty_buf, sizeof(_dirty_buf));

Under such a fast data flow, broadcast_slave must use the frame_length parameter in agile_modbus_slave_handle to handle sticky packets.

Enter the build/bin directory and open Linux Shell. The demonstration effect is as follows