I2C Modbus RTU Master Chip – IS4320

Description

The IS4320 is an integrated circuit with a built-in Modbus RTU Master Stack, providing a complete standalone Modbus Master solution with an I2C-Serial interface for easy integration into customer applications.

The IS4320 enables any I2C Master device to communicate with Modbus RTU slave devices, allowing data to be read using Function Codes 1, 2, 3, and 4, or written using Function Codes 15 and 16. Its simplicity of use through the I2C-Serial Interface drastically reduces firmware development time while providing a robust Modbus solution.

The IS4320 features two communication buses: a TTL UART for Modbus and an I2C-Serial Interface for the microcontroller. The Modbus UART can connect to various transceivers such as RS485, RS422, RS232, fiber, or radio, with RS485 being the most common. The I2C-Serial Interface connects to any I2C Master device, including microcontrollers, microprocessors, single-board computers like the Raspberry Pi, or development boards such as Arduino.

The IS4320 operates at 3.3V, and its Modbus UART and I2C pins are 5V tolerant, allowing the chip to connect with a wide variety of RS485 transceivers and microcontrollers.

It is available in Industrial (-40ºC to +85ºC) and Extended Temperature Range (-40º to +125ºC).

The IS4320 offers a ready-to-use Modbus stack solution that helps reduce development time and speed up your time-to-market, while fully complying with strict T1.5 and T3.5 protocol timing requirements.

How Does It Work?

Essentially, you write the desired Modbus request into the IS4320 Memory Map and it will be sent to the Slave, then read back the Memory Map to get the received response.

The IS4320 operates very simply via I2C in three steps. All operations are performed using I2C Word Write and I2C Word Read operations. These commands are the same ones typically used to access I2C EEPROMs and are already implemented in most microcontroller IDEs, such as STM32CubeIDE or Arduino.

• 1. Configure the IS4320 Modbus communications: Set the baud rate, parity, and stop bits to match the Modbus Slave device configuration by writing to the following registers: CFGMBBDR, CFG_MBPAR, and CFG_MBSTP.
• 2. Configure and execute the Modbus Request: Set the Slave ID, the Function Code, the Starting Address for the read or write operation, and the Quantity of registers. If performing a write operation, also set the data to be written. Finally, trigger the Request. This is done using the following registers: REQ_SLAVE, REQ_FC, REQ_STARTING, REQ_QTY and REQ_EXECUTE. Use also REQ_DATAx for a write operation.
• 3. Read the Modbus Response: After executing the Request, you can check the result of the operation by reading the RES_STATUS register. If you Requested to read some data, retrieve also the data by reading the RES_DATAx registers.

Default Chip Settings

Default Modbus Settings:

• Modbus Baud Rate: 19200 bps
• Modbus Parity: Even
• Modbus Stop Bits: 1

Default I2C Settings:

• I2C Slave Address: 0x14
• I2C Speed: Depends on pin 7: 100 kHz (pin 7 to GND), 400 kHz (pin 7 to 3.3V/2), 1 MHz (pin 7 to 3.3V)

Need an Evaluation Board?

• For Arduino and STM32 Nucleo Boards: Kappa4320Ard is an Arduino-form-factor evaluation board that lets you prototype and experiment with the Modbus chip IS4320 over RS485.
• For Raspberry Pi and other single board computers: The Kappa4320Rasp is a Raspberry Pi-form-factor evaluation board that lets you prototype and experiment with the Modbus chip IS4320 over RS485. The IS4320 time deterministic stack allows a correct management of the T15 and T35 critical timings, that’s specially relevant on non-deterministic systems like computers.

For more information about the Evaluation Board you can also check: www.inacks.com/is4320

This company and the products provided herein are developed independently and are not affiliated with, endorsed by, or associated with any official protocol or standardization entity. All trademarks, names, and references to specific protocols remain the property of their respective owners.