Pinout
SCL and SDA Pads
I2C-Compatible Bus Interface Pads.
Both pads are open-drain and must be pulled up to 3.3V or 5V. The pull-up resistor value should be chosen based on the bus speed and capacitance. Typical values are 4.7kΩ for Standard Mode (100kbps) and 2.2kΩ for Fast Mode (400kbps) at both 3.3V and 5V.
+5V Pad
Module Power Supply Pad.
This pad is the power input for the entire module. The module includes an LDO to regulate the voltage down to 3.3V for the IS4310 power supply.
5V must be supplied to this pad. Bypass capacitors are included on the module, no need to place them outside of the module.
PWR Pad
Bus Power Supply Pad.
The Modbus Serial Line Bus can optionally carry power to its connected devices. When using RJ45 connectors, the Bus Power Supply is on pin 2. The bus voltage can range from 5V to 24V.
This module daisy-chains the Bus Power Supply from one RJ45 connector and routes it to this pad.
This PWR Pad allows your design to be self-powered from the bus, eliminating the need for an external power supply. If designing a self-powered Slave, please note that not all Modbus Serial Line Buses carry power, and proper voltage regulation must be implemented on the PWR Pad.
The maximum daisy-chained current is 750mA. The module includes a resettable fuse to limit the current.
GND Pads
Module Ground.
The GND pads the 0V of the module.
These pads are also connected to the Common signal of the RS485 bus and therefore serve as the return path for the PWR Pad.
The common signal of the RS485 bus must be connected to protective ground, preferably at a single point. The recommended location is at the master device.
GND pads are not connected to the shield of the RS485 cables and connectors, as all shields should be connected to protective ground at a single point for the entire bus, ideally at the master device.
The module has multiple GND pads, all of which must be soldered to ensure proper mechanical attachment of the module to the main PCB. This is especially important when the RJ45 connectors are plugged in, as a significant amount of force is applied to the module. Failing to solder all pads or poor soldering can cause the module to detach from the main PCB.
I2CSPD Pad
I2C-Serial Interface Speed Selection Pad.
This pad is directly connected to the pin I2CSPD of the IS4310. It configures the IS4310 internal I2C-Serial Interface timings and filters to properly work with the selected bus speed.
- For a 100kHz setting, set the I2CSPD pad to GND.
- For a 400kHz setting, set the I2CSPD to 1.65V using a voltage divider. This can be achieved using a 6.8kΩ and a 3.3kΩ resistors from the I2CSPD pad: one to 5V and the other to GND. Please note that applying a voltage higher than 3.3V to I2CSPD pad would permanently damage the IS4310 IC.
- For a 1000MHz setting, set the I2CSPD pad to 3.3V. Please note that pulling I2CSPD to 5V would permanently damage the IS4310 IC.
Important Remark:
A mismatch between the configured I2C speed and the actual operating I2C speed (e.g., configuring the bus for 100kHz but operating at 1MHz) can lead to an inconsistent state where some I2C messages are processed while others are not.
Ensure a proper match between the actual operating speed and the configured speed at the I2CSPD pad: If your bus works at 100kHz, ensure the I2CSPD pad is tied to VSS. If it works at 400kHz ensure the pad is at 1.65V. If it works at 1000MHz, ensure the pad is at 3.3V.
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