IND-MOD-IO88

Electrical Safety

Risk of Electric Shock

The IND-MOD-IO88 is intended for use with industrial control systems. Incorrect installation or wiring may result in electric shock, equipment damage, or personal injury.

Disconnect all power sources before installing or servicing the module.
Verify that the power supply is turned off before making or modifying any wiring connections.
Never touch exposed conductors while the system is energized.

Qualified Personnel Only

Installation, commissioning, and maintenance of this product must only be performed by qualified personnel familiar with industrial electrical systems and local electrical safety regulations.

Observe Voltage Ratings

Ensure that all input voltages, output loads, and power supply connections remain within the specifications provided in this manual. Exceeding the maximum ratings may permanently damage the module.

Wiring

Use appropriately sized wires and tighten terminal screws securely.
Verify wiring polarity before applying power.
Keep signal wiring separate from high-voltage or high-current cables to reduce electrical noise.

Regulatory Compliance

Follow all applicable local electrical codes and safety standards when installing and operating the IND-MOD-IO88.

Introduction

The IND-MOD-IO88 is a compact industrial Modbus RTU 8-channel I/O Module designed to simplify the integration of digital inputs and outputs into PLC, SCADA, HMI, and Industrial IoT systems. It communicates over the industry-standard RS-485 interface using the Modbus RTU protocol, ensuring reliable interoperability with a wide range of industrial automation equipment.

The module provides 8 opto-isolated digital inputs and 8 opto-isolated digital outputs, making it suitable for monitoring field devices such as push buttons, limit switches, proximity sensors, and relay contacts, while simultaneously controlling loads including relays, contactors, indicator lamps, solenoid valves, and other industrial actuators.

Designed for demanding industrial environments, the IND-MOD-IO88 supports both dry-contact and wet-contact (up to 24 VDC) digital inputs (NPN or PNP) with built-in bidirectional optocoupler and 8 Digital Outputs supports upto 40V, open-drain output, output load 500mA/channel(MAX) allowing seamless integration with a wide variety of sensors and control devices. The robust RS-485 communication interface enables reliable long-distance communication in electrically noisy environments.

Whether used as a distributed remote I/O module, a PLC expansion module, or an interface between field devices and Industrial IoT gateways, the IND-MOD-IO88 offers a cost-effective, reliable, and easy-to-deploy solution for industrial automation applications.

Key Features

8 opto-isolated digital inputs
Supports both dry-contact and wet-contact inputs (up to 24 VDC)
8 opto-isolated digital outputs for controlling external loads
RS-485 communication with Modbus RTU protocol
Compatible with PLCs, HMIs, SCADA systems, and Industrial IoT gateways
Long-distance, noise-immune industrial communication
Compact DIN-rail mount enclosure
Easy configuration and integration into existing Modbus networks

Typical Applications

PLC I/O expansion
Remote monitoring and control
Factory automation
Process automation
Building management systems (BMS)
Water and wastewater treatment
Energy monitoring and control
Industrial IoT and edge gateway applications

Technical Specifications

Parameter	Specification
Communication Interface	RS-485
Protocol	Modbus RTU (Standard Modbus RTU Protocol)
Supported Baud Rates	4800, 9600, 19200, 38400, 57600, 115200, 128000, 256000 bps
Default Communication Settings	9600 bps, 8 Data Bits, No Parity, 1 Stop Bit (8-N-1)
Power Supply	7–28 VDC
Digital Inputs	8 Channels
Input Voltage Range	5–24 VDC
Input Type	Supports Dry Contact, NPN (Sinking), and PNP (Sourcing) Inputs
Input Isolation	Built-in Bidirectional Optocoupler Isolation
Digital Outputs	8 Channels
Output Type	Open-Drain (Low-Side Switching)
Output Voltage Range	5–40 VDC
Maximum Output Current	500 mA per Channel (Maximum)
Modbus Slave Address	Configurable from 1 to 255
Default Slave Address	1 (0x01)

Wiring

Terminal Assignment

Terminal	Description	Terminal	Description
PWR IN	Power Supply Positive (+)	RS485+	RS-485 Data A
GND	Power Supply Ground (-)	RS485-	RS-485 Data B
NC	Not Connected	EARTH	RS-485 Shield / Earth Ground
DGND	Signal Ground	DGND	Signal Ground
DI7	Digital Input Channel 8	DO7	Digital Output Channel 8
DI6	Digital Input Channel 7	DO6	Digital Output Channel 7
DI5	Digital Input Channel 6	DO5	Digital Output Channel 6
DI4	Digital Input Channel 5	DO4	Digital Output Channel 5
DI3	Digital Input Channel 4	DO3	Digital Output Channel 4
DI2	Digital Input Channel 3	DO2	Digital Output Channel 3
DI1	Digital Input Channel 2	DO1	Digital Output Channel 2
DI0	Digital Input Channel 1	DO0	Digital Output Channel 1
DI COM	Common Terminal for Digital Inputs	DO COM	Common Terminal for Digital Outputs

Digital Input Wiring

The IND-MOD-IO88 supports three types of digital input connections:

Dry Contact (Passive Input)
NPN Sensor (Sinking Input)
PNP Sensor (Sourcing Input)

DI COM Configuration

The DI COM terminal determines how the digital inputs operate.

DI COM Connection	Input Mode
Not Connected	Dry Contact (Passive) Input
Connected to +V	NPN (Low-Level Active) Input
Connected to GND	PNP (High-Level Active) Input

Note

The digital input voltage range is 5–24 VDC.

Digital Output Wiring

The digital outputs are Open-Drain (Low-Side Switching) outputs.

Connect DO COM to the positive terminal of the output power supply.

The output load should be connected between DO COM (+V) and the corresponding DOx output.

Warning

Each digital output can sink up to 500 mA maximum. Exceeding this rating may permanently damage the output driver.

RS-485 Wiring

Terminal	Description
RS485+	RS-485 Data A
RS485-	RS-485 Data B
EARTH	Cable Shield / Earth Ground (Recommended)

Tip

Use twisted-pair cable for RS-485 communication.
Connect the cable shield to EARTH at one point only.
Terminate both ends of the RS-485 bus with 120 Ω resistors when required.
Avoid running RS-485 cables alongside high-voltage or high-current wiring.

Power Supply

Terminal	Description
PWR IN	Positive Supply (7-28V)
GND	Negative Supply

Warning

Verify the power supply polarity before powering the module. Reverse polarity may damage the device.

Operation Protocol

Function Code

Function Code	Description	Note
01	Read Coil Status	Read digital output status
02	Read Discrete Inputs	Read digital input status
03	Read Holding Registers	Read device configuration parameters
05	Write Single Coil	Control a single output
06	Write Single Holding Register	Write device configuration
0F	Write Multiple Coils	Control multiple outputs
10	Write Multiple Registers	Write multiple device configuration parameters

Register Address

Address (HEX)	Description	Register Value	Access	Function Code
0x0000 .... 0x0007	Digital Ouput from DO0 to DO7	0x0000 = OFF 0xFF00 = ON	Read/Write	0x01, 0x05, 0x0F
1x0000 .... 1x0007	Digital Input from DI0 to DI7	0 = OFF 1 = ON	Read	0x02
4x0000	Modbus Slave Address	1 ~ 247	Read/Write	0x03, 0x06, 0x10
4x0001	Baud Rate	See Baud Rate Table	Read/Write	0x03, 0x06, 0x10

Note

Function Code 0x0F (Write Multiple Coils) uses the same starting addresses (0x0000–0x0007) but writes multiple coil states in a single Modbus request.

Baudrate Table

Baudrate	Register Value
4800	0
9600 (Default)	1
19200	2
38400	3
57600	4
115200	5
128000	6
256000	7

Modbus Communication Examples

The examples below assume the module is operating at its default Slave Address (0x01). All data frames are represented in Hexadecimal (HEX).

Understanding the Frame Structure

Every Modbus RTU frame follows a standard structure: [Slave Address] [Function Code] [Data/Address bytes...] [CRC Low] [CRC High]

0x01: Read Coil Status (Read Digital Outputs)

Used to read the current ON/OFF status of the digital outputs (DO0 to DO7).

Example: Read the status of all 8 digital outputs (Starting address 0x0000, Quantity 8).

Request Frame: 01 01 00 00 00 08 3D CC
01: Slave Address
01: Function Code
00 00: Starting Address (DO0)
00 08: Quantity of Coils to read (8)
3D CC: CRC16
Response Frame: 01 01 01 05 91 8B
01: Slave Address
01: Function Code
01: Byte Count (1 byte returned)
05: Data (0x05 = Binary 00000101, meaning DO0 and DO2 are ON, the rest are OFF)
91 8B: CRC16

0x02: Read Discrete Inputs (Read Digital Inputs)

Used to read the current state of the digital inputs (DI0 to DI7).

Example: Read the status of all 8 digital inputs (Starting address 0x0000, Quantity 8).

Request Frame: 01 02 00 00 00 08 79 CC
01: Slave Address
02: Function Code
00 00: Starting Address (DI0)
00 08: Quantity of Inputs to read (8)
79 CC: CRC16
Response Frame: 01 02 01 03 E1 89
01: Slave Address
02: Function Code
01: Byte Count
03: Data (0x03 = Binary 00000011, meaning DI0 and DI1 are currently triggered)
E1 89: CRC16

0x03: Read Holding Registers (Read Configuration)

Used to read the device's configuration parameters, such as the Slave Address and Baud Rate. (Note: When querying Modbus over the wire, the 4x prefix is omitted; address 4x0000 is transmitted as 0x0000).

Example: Read both the Slave Address and Baud Rate (Starting address 0x0000, Quantity 2).

Request Frame: 01 03 00 00 00 02 C4 0B
01: Slave Address
03: Function Code
00 00: Starting Address (Slave Address Register)
00 02: Quantity of Registers to read (2)
C4 0B: CRC16
Response Frame: 01 03 04 00 01 00 01 6B F3
01: Slave Address
03: Function Code
04: Byte Count (2 registers = 4 bytes)
00 01: Data 1 (Slave Address = 1)
00 01: Data 2 (Baud Rate = 1, corresponding to 9600 bps)
6B F3: CRC16

0x05: Write Single Coil (Control a Single Output)

Used to turn a single digital output ON or OFF. According to the standard Modbus RTU protocol, 0xFF00 turns the output ON, and 0x0000 turns it OFF.

Example: Turn ON Digital Output 1 (DO0, Address 0x0000).

Request Frame: 01 05 00 00 FF 00 8C 3A
01: Slave Address
05: Function Code
00 00: Register Address (DO0)
FF 00: Data (ON)
8C 3A: CRC16
Response Frame: 01 05 00 00 FF 00 8C 3A (The device perfectly echoes the request upon success)

0x06: Write Single Holding Register (Change Configuration)

Used to write configuration parameters, such as changing the Slave Address or Baud Rate.

Example: Change the Baud Rate to 115200 bps (Register 0x0001, Value 5).

Request Frame: 01 06 00 01 00 05 18 09
01: Slave Address
06: Function Code
00 01: Register Address (Baud Rate)
00 05: Data Value (5 = 115200 from the Baudrate Table)
18 09: CRC16
Response Frame: 01 06 00 01 00 05 18 09 (The device echoes the request upon success)

Warning

A power cycle or module reboot may be required before the new Baud Rate or Slave Address takes effect.

0x0F: Write Multiple Coils (Control Multiple Outputs)

Used to set the ON/OFF status of several digital outputs simultaneously in a single command.

Example: Turn ON DO0, DO1, and DO2, and turn OFF DO3 through DO7.

Request Frame: 01 0F 00 00 00 08 01 07 3E 95
01: Slave Address
0F: Function Code
00 00: Starting Address (DO0)
00 08: Quantity of Coils (8)
01: Byte Count (1 byte of data to follow)
07: Data (0x07 = Binary 00000111, meaning DO0, DO1, DO2 are ON)
3E 95: CRC16
Response Frame: 01 0F 00 00 00 08 54 0D
01: Slave Address
0F: Function Code
00 00: Starting Address
00 08: Quantity of Coils written
54 0D: CRC16