Connect Modbus TCP

Proxus provides a high-performance Modbus TCP driver capable of batch reading and automatic byte swapping.

Supported Protocol Variants

Protocol Type	Description
`Modbus_Tcp`	Standard Modbus TCP
`Modbus_Rtu_OverTcp`	Modbus RTU encapsulated over TCP
`ModbusAscii_OverTcp`	Modbus ASCII encapsulated over TCP

Connection Parameters

Basic Settings

Parameter	Type	Required	Default	Description
Host	string	Yes	-	IPv4 address of the PLC or Gateway
Port	int	No	`502`	Standard Modbus TCP port
PollingInterval	int	No	`1000`	Read cycle interval in milliseconds
ConnectTimeout	int	No	`3000`	Connection timeout (ms)
ReceiveTimeout	int	No	`3000`	Response timeout (ms)

Modbus-Specific Settings

Parameter	Type	Default	Description
Station	byte	`1`	Unit ID / Slave ID (1-255)
AddressStartWithZero	bool	`true`	Use 0-based addressing
DataFormat	enum	`ABCD`	Byte order (ABCD, DCBA, BADC, CDAB)
IsStringReverse	bool	`false`	Reverse string byte order
IsCheckMessageId	bool	`true`	Validate response message ID
Crc16CheckEnable	bool	`true`	Enable CRC16 check (RTU only)

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Station ID

The Station parameter (Unit ID) is critical when connecting through a Modbus gateway to multiple devices. Each device behind the gateway has a unique Station ID.

Converting Datasheet Addresses

Device datasheets often use different addressing conventions. Here's how to convert them to Proxus format:

Common Datasheet Formats

Datasheet Format	Meaning	Proxus Format
`40001`	Holding Register 1	`x=3;0`
`40100`	Holding Register 100	`x=3;99`
`30001`	Input Register 1	`x=4;0`
`30100`	Input Register 100	`x=4;99`
`00001`	Coil 1	`x=1;0`
`10001`	Discrete Input 1	`x=2;0`
`HR100` / `4x100`	Holding Register 100	`x=3;99`
`IR50` / `3x50`	Input Register 50	`x=4;49`

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1-Based vs 0-Based

Most device datasheets use 1-based addressing (first register = 1), but Modbus protocol uses 0-based addressing (first register = 0).

Always subtract 1 from datasheet addresses:

Datasheet says 40100 → Proxus: x=3;99
Datasheet says 30050 → Proxus: x=4;49

Conversion Formula

Proxus Address = Datasheet Address - Base - 1

Where Base:
40001 series → Base = 40000 (Holding Registers, FC03)
30001 series → Base = 30000 (Input Registers, FC04)
10001 series → Base = 10000 (Discrete Inputs, FC02)
00001 series → Base = 0 (Coils, FC01)

Real-World Examples

Device/Sensor	Datasheet Says	Proxus Address	Data Type
Energy Meter - Voltage	`30001`	`x=4;0`	Float
Energy Meter - Current	`30003`	`x=4;2`	Float
VFD - Motor Speed	`40201`	`x=3;200`	UShort
VFD - Run Command	`00001`	`x=1;0`	Bool
Temperature Sensor	`30101`	`x=4;100`	Short

Address Syntax

Proxus supports flexible address formats for all Modbus function codes.

Basic Format

The simplest format is just the register address:

{address}

Example: 100 reads register 100 using the default function code (03 for Holding Registers).

Extended Format

For explicit control over station ID and function code:

s={station};x={function};{address}

Component	Description	Values
`s=`	Station/Slave ID	1-255
`x=`	Function Code	1, 2, 3, 4
`w=`	Write Function Code (optional)	5, 6, 15, 16
`{address}`	Register address	0-65535

Examples

Address	Description
`100`	Register 100, default function code
`x=3;100`	Holding Register 100 (FC03)
`x=4;100`	Input Register 100 (FC04)
`s=2;100`	Register 100 on Slave ID 2
`s=2;x=3;100`	Holding Register 100 on Slave ID 2
`s=5;x=4;500`	Input Register 500 on Slave ID 5

Function Codes

Code	Area	Access	Description
01	Coils	Read/Write	Discrete outputs (bits)
02	Discrete Inputs	Read Only	Discrete inputs (bits)
03	Holding Registers	Read/Write	16-bit registers
04	Input Registers	Read Only	16-bit input registers

Standard Notation Mapping

If you prefer traditional 5-digit or 6-digit Modbus notation:

Notation	Function Code	Proxus Equivalent
`000001` - `009999`	FC01 (Coils)	`x=1;0`
`100001` - `109999`	FC02 (Discrete Inputs)	`x=2;0`
`300001` - `309999`	FC04 (Input Registers)	`x=4;0`
`400001` - `409999`	FC03 (Holding Registers)	`x=3;0`

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Recommendation

Use the explicit x={function};{address} format to avoid ambiguity. Different vendors interpret standard notation differently.

Data Types

Multi-register values are automatically reconstructed from consecutive registers.

Type	Size	Registers	Description
Bool	1 bit	N/A	Coils or Discrete Inputs
Short	16 bit	1	Signed integer
UShort	16 bit	1	Unsigned integer
Int	32 bit	2	Signed 32-bit integer
UInt	32 bit	2	Unsigned 32-bit integer
Long	64 bit	4	Signed 64-bit integer
ULong	64 bit	4	Unsigned 64-bit integer
Float	32 bit	2	IEEE 754 single precision
Double	64 bit	4	IEEE 754 double precision
String	Variable	N	ASCII string (requires length)

Byte Order

Different devices use different byte ordering for multi-register values. Configure the ByteOrder in the Device Profile:

Setting	Description	Example (0x12345678)
`ABCD`	Big Endian	`12 34 56 78`
`DCBA`	Little Endian	`78 56 34 12`
`BADC`	Mid-Big Endian	`34 12 78 56`
`CDAB`	Mid-Little Endian	`56 78 12 34`

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Scrambled Values

If Float or Int32 values appear extremely large, small, or nonsensical, the byte order is likely incorrect. Try different ByteOrder settings.

Performance Features

Batch Reading

The driver automatically groups contiguous addresses into single requests:

Registers 100, 101, 102, 103 → Single read request
Gaps larger than 2 registers break the batch
Dramatically reduces network round-trips

Polling Intervals

Configure different polling rates for different registers. Fast-changing values (e.g., motor speed) can poll at 100ms while slow-changing values (e.g., temperature) poll at 5000ms.

Industry Use Cases

Modbus is our most versatile driver, utilized extensively across multiple industries:

Manufacturing: Integrating legacy PLCs, VFDs (Variable Frequency Drives), and simple IO blocks.
Energy & Utilities: Real-time data acquisition from power meters, solar inverters, and battery management systems.
Mining: Monitoring ventilation fans, pumps, and crushers to optimize extraction efficiency. sub-meters.

Troubleshooting

Error	Cause	Solution
Timeout	Device not responding	Check IP, Port, Station ID
Illegal Data Address	Register doesn't exist	Verify register number in device manual
Illegal Function	Function code not supported	Use correct function code for data area
Gateway Path Unavailable	Wrong Station ID	Verify Unit ID for device behind gateway
Timeout	PollingInterval too short	Increase PollingInterval or check network latency
Checksum Error	Noise or wrong settings	Verify Baud Rate, Parity (RTU) or check interference