HollySys Modbus RTU

The EMQX Neuron HollySys Modbus RTU driver is for collecting HollySys PLC tags using the Modbus RTU protocol,

For the generic steps, see Create a Southbound Driver and Groups and Tags.

Add Driver

On Data Collection → South Devices, click Add Device.

• Name: The name of this device node.
• Driver: Select the HollySys Modbus RTU driver.

Connection Parameters

Click the driver card to open the Device Configuration page and fill in:

Parameter	Description
Physical Link	Selects the communication medium, either serial or Ethernet.
Connection Timeout	The time the system waits for a device to respond to a command.
Maximum Retry Times	The maximum number of retries after a failed attempt to send a read command.
Retry Interval	Resend reading instruction interval(ms) after a failed attempt to send a read command.
Send Interval	The 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 Device	Only needed in Serial mode, the path to the serial device when using a serial connection, e.g., /dev/ttyS0 in Linux systems.
Stop Bits	Only for the Serial mode, the serial connection parameter.
Parity	Only for the Serial mode, the serial connection parameter.
Baud Rate	Only for the Serial mode, the serial connection parameter.
Data Bits	Only for the Serial mode, the serial connection parameter.
Connection Mode	Only for the Ethernet mode, you can choose EMQX Neuron as the TCP client or server.
IP Address	Only for the Ethernet mode, the IP address of the device when using TCP connection with EMQX Neuron as the client, or the IP address of EMQX Neuron when using TCP connection with EMQX Neuron as the server. The default value is 0.0.0.0.
Port	Only for the Ethernet mode, the port number of the device when using TCP connection with EMQX Neuron as the client, or the port number of EMQX Neuron when using TCP connection with EMQX Neuron as the server.
Maximum Retry Times	The maximum number of retries after a failed attempt to send a read command.
Retry Interval	Resend reading instruction interval(ms) after a failed attempt to send a read command.

The HollySys Modbus RTU driver configuration is similar to that of the Modbus RTU driver module.

Tag Configuration

The data types and address formats supported by this driver are listed below.

Data types

• BIT
• BOOL
• INT16
• UINT16
• WORD

Address format

SLAVE!ADDRESS[#ENDIAN]

The address format is nearly the same to that of the Modbus RTU driver module, the only difference is in the ADDRESS part.

SLAVE

Required, Slave is the slave address or site number.

ADDRESS

HollySys PLC maps data units onto the Modbus address space for access through the Modbus RTU protocol. The EMQX Neuron HollySys Modbus RTU driver frees users from details of the address mapping, and designates the PLC data unit name as the ADDRESS.

Area	Data unit example	Attribute	Register Size	Data Type
IX (Input)	IX0.0 ... IX0.7, IX1.0 ... IX1.7 ...	Read	1Bit	BOOL/BIT
IW (Input Registers)	IW0, IW1, ...	Read	16Bit,2Byte	INT16/UINT16
QX (Coils)	QX0.0 ... QX0.7, QX1.0 ... QX1.7 ...	Read/Write	1Bit	BOOL/BIT
QW (Hold Registers)	QW0, QW1, ...	Read/Write	16Bit,2Byte	INT16/UINT16
MX (Coils)	MX0.0 ... MX0.7, MX1.0 ... MX1.7 ...	Read/Write	1Bit	BOOL/BIT
MW (Hold Registers)	MW0, MW1, ...	Read/Write	16Bit,2Byte	INT16/UINT16

#ENDIAN

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

Symbol	Byte Order	Supported Data Types	Note
#B	2,1	int16/uint16
#L	1,2	int16/uint16	Default byte order if not specified

TIP

The byte order can be illustrated using the notation ABCD, which corresponds directly to the sequence 1234. As an example, the ABCD designation represents the standard or default Endianness 1234. (#LL).

Example Addresses

Address	Data Type	Description
1!IX1.0	bit	Data unit IX1.0 on slave 1, read only.
1!QW0	int16	Data unit QW0 on slave 1, support read/write.
2!MW1	int16	Data unit MW1 on slave 1, support read/write.