ISXMPL4350ex2 - IS4350 I2C Modbus TCP Server Simple Example for Arduino

A minimal Arduino Uno example for the IS4350, the I2C Modbus TCP/IP Server chip by INACKS.

The sketch brings the Modbus TCP server online and increments Holding Register 0 (HOLD_0) by 1 every second. Any Modbus TCP client (a PLC, SCADA system or PC tool) can read the value over Ethernet.

No dedicated library is needed: the sketch uses only the standard Arduino Wire library and two short routines, one to read a register and one to write it.

What the sketch does

1. Writes an initial value to HOLD_0, so clients never read invalid data.
2. Brings the Modbus server online by writing 1 to the GO_ONLINE register.
3. Waits until the STATUS register reads 5 (Modbus server ready and listening).
4. Increments HOLD_0 every second.

By default, the IS4350 uses DHCP and a MAC address generated from its serial number, so no network configuration is needed.

Hardware

• Arduino Uno
• IS4350 (or the IS4350-M1 module)
• 2 × 4.7 kΩ pull-up resistors
• Ethernet connection to a network with a DHCP server

Wiring

Arduino Uno	IS4350	Notes
A4 (SDA)	SDA	4.7 kΩ pull-up to 5 V
A5 (SCL)	SCL	4.7 kΩ pull-up to 5 V
GND	VSS	Common ground
—	ADR → GND	I2C address 24 (0x18)
—	SPD → GND	100 kHz (Arduino Wire default)

Usage

1. Open the .ino file in the Arduino IDE.
2. Select Arduino Uno and upload.
3. Open the Serial Monitor at 9600 baud.

Expected output:

STATUS: 3
STATUS: 5
Server online.
HOLD_0 = 1
HOLD_0 = 2
...

4. Read Holding Register 0 from any Modbus TCP client on port 502. Use the IS4350's IP address, which you can read from its IP registers.

Key points

• Register addresses and register values are 16-bit and are sent MSB first.
• Reads use a repeated start (Wire.endTransmission(false)).
• Leave a few milliseconds between consecutive I2C operations.
• GO_ONLINE is 0 after every power-up, so the sketch sets it at startup.
• If STATUS shows an error (101 and above), check the network cable and the MAC configuration. See the datasheet for the full list of status codes.

Documentation

• IS4350 datasheet and product page: www.inacks.com/is4350
• IS4350-M1 module: www.inacks.com/is4350-m1