24 DI / 24 DO

24DI / 24DO Modbus Remote I/O Module

Compact Modbus RTU remote I/O module with twenty-four digital inputs and twenty-four digital NPN outputs with configurable ON/OFF delay control.

Key Features

• 24 Digital Inputs, 24V compatible
• 24 Digital NPN Outputs
• All inputs have latched status – Never miss an input change
• All inputs have individual counter functions with retentive memory storage
• Configurable digital output ON delay and OFF delay
• Modbus RTU over RS-485
• Rotary address switch for address selection from 1 to 99
• Wide supported baud rates from 300 to 115200
• DIN rail or wall mountable
• Dimensions: 110 mm × 140 mm × 85 mm (L × W × H)

ModViz – Modbus Configuration & Visualization Tool

ModViz is a powerful yet simple configuration and visualization tool designed to work seamlessly with Veawe Modbus I/O modules. It enables engineers, system integrators, and technicians to quickly configure, monitor, and test field devices through an intuitive graphical interface.

The software can be downloaded from https://veawe.io/modviz/

Ordering Information

Product Code	Description
UIO-24DI-24DO	24-Channel Digital Input / 24-Channel Digital Output Modbus Remote I/O Module
UIO-12DI-12DO	12-Channel Digital Input / 12-Channel Digital Output Modbus Remote I/O Module
UIO-24DI	24-Channel Digital Input Modbus Remote I/O Module
UIO-24DO	24-Channel Digital Output Modbus Remote I/O Module
UIO-4DI-4DO	4-Channel Digital Output and Input Modbus Remote I/O Module
UIO-8DI	8-Channel Digital Input Modbus Remote I/O Module

Applications

• Reading 24 digital PNP input signals and simultaneously controlling 24 NPN outputs from a single Modbus module
• Counting pulses from flow meters, encoders, and proximity sensors with retentive memory
• Driving relays, solenoids, and indicator lamps with configurable per-channel ON/OFF delay
• Building compact Modbus I/O expansion for PLCs and SCADA systems where both input and output are needed
• Replacing traditional timer relays with software-configurable delay logic on each output channel

Specifications

Parameter	Value
Mounting	DIN rail or wall mountable
Dimensions	110 mm × 140 mm × 85 mm (L × W × H)

Electrical Specifications

Parameter	Value
Supply Voltage	15–24V DC
Digital Output Rating	24VDC 500mA max, NPN Control
Digital Input Voltage	15–24V DC, PNP Inputs
Communication Port	RS-485

Input/Output Specifications

Parameter	Value
Digital Input Channel Count	24
Input Type	Digital PNP, 24V compatible
Digital Output Channel Count	24
Output Type	Digital NPN
Slow Counter Speed	Up to 1 kHz
Counter Memory	Retentive on power cycles
ON/OFF Delay Resolution	10 ms (1 count = 10 ms)
Maximum Output Delay	655.35 seconds (65535 counts)

Isolation & Protection Specifications

Parameter	Value	Notes / Description
Supply Reverse Polarity Protection
Supply Isolation
Transient Voltage Clamping
EMC & Immunity Standards
RS-485 Bus ESD Protection

Mechanical Dimensions

Terminal Details

Top Connector – RS-485

Pin	1	2	3	4	5
Signal	A	B	Shield	NC	NC

Bottom Connector – Power

Pin	1	2
Signal	24V	GND

Digital Input Connector

Pin	Signal
1–12	X1–X12
13–24	X13–X24

Digital Output Connector

Pin	Signal
1–12	Y1–Y12
13–24	Y13–Y24

Wiring Diagrams

Note: All images and connection diagrams shown are for illustrative purposes only and may differ from the actual product.

Communication Interface

Protocol	Physical Layer	Default Baud Rate	Default Format
Modbus RTU	RS-485	19200	8N1

Basic Process Registers

Signal	Address	Type	Description
DI1–DI24	10001–10024	Bit	DI1 to DI24 live digital input status
DO1–DO24	00001–00024	Bit	DO1 to DO24 output control and status

Supported Modbus Function Codes

Read	Write
01 – Read Coils	05 – Write Single Coil
02 – Read Discrete Inputs	06 – Write Single Register
03 – Read Holding Registers	15 – Write Multiple Coils
04 – Read Input Registers	16 – Write Multiple Registers

Register Map Overview

Function	Address Range	Type	Description
Discrete Inputs	10001–10024	Bit	DI1 to DI24 live digital input status
Discrete Inputs	10201–10224	Bit	DI1 to DI24 latched status, auto-clears on read
Coils	00001–00024	Bit	DO1 to DO24 digital output control and status
Coils	00251–00274	Bit	Reset DI1 to DI24 slow counters
Coils	00401–00424	Bit	Pending DO1 to DO24 delay status and override
Input Registers	30251–30274	int16	DI1 to DI24 slow counter values (1 kHz)
Holding Registers	40401–40424	int16	DO1 to DO24 ON delay
Holding Registers	40451–40474	int16	DO1 to DO24 OFF delay
Holding Registers	40101	int16	Modbus server (slave) address

Detailed Register Tables

Discrete Inputs (1xxxx)

Digital Live Input Status

Address	Type	Description
10001–10024	Bit	DI1 to DI24 live digital input status

Digital Latched Input Status

Address	Type	Description
10201–10224	Bit	DI1 to DI24 latched status, auto-clears on read

Latched input status stays high even after the input goes low and auto-clears only after the master reads this bit. This ensures no input state change is missed by the controller.

Coils (0xxxx)

Digital Output Control

Address	Type	Description
00001–00024	Bit	DO1 to DO24 digital output control and status

Slow Counter Reset

Address	Type	Description
00251–00274	Bit	Reset DI1 to DI24 slow counter

Writing 1 to the coil resets the corresponding slow counter value. This bit is self-clearing and the reset value is not stored on power cycle.

Pending Output State

Address	Type	Description
00401–00424	Bit	Pending DO1 to DO24 state while ON/OFF delay timer is active

Writing 1 to a pending coil overrides the delay timer and immediately switches the output ON.

Input Registers (3xxxx)

Digital Inputs Slow Counter Values

Address	Type	Description
30251–30274	int16	DI1 to DI24 slow counter, up to 1 kHz (Retentive memory on power cycles)

DI state changes are counted and stored in these registers. Counter values are retained across power cycles.

Holding Registers (4xxxx)

Digital Output Delay Configuration

Address	Type	Description
40401–40424	int16	DO1 to DO24 ON delay
40451–40474	int16	DO1 to DO24 OFF delay

Delay Resolution: 1 = 10 ms, 100 = 1 second. Maximum value: 65535 = 655.35 seconds.

Communication Settings

Address	Type	Description
40101	int16	Modbus server (slave) address (switch value)
40102	int16	Baud rate selection
40103	int16	Serial format selection
40106	int16	Watchdog interval. Example: 10 = 1 second
40107	int16	Watchdog action. 0 = Modbus Watchdog Disabled, 1 = Reset Outputs on Modbus Watchdog Expire

Modbus Address (40101)

This is set using the rotary or DIP switches.

Baud Rate Register (40102) and Serial Format Register (40103)

Value	Baud Rate	Value	Baud Rate	Value	Format
0	300	7	9600	0	8N1
1	600	8	14400	1	8E1
2	1200	9	19200	2	8O1
3	1800	10	38400	3	8N2
4	2400	11	57600	4	8E2
5	4800	12	62500	5	8O2
6	7200	13	115200

Default: 19200 baud, 8N1.

Default Settings

Setting	Default
Slave Address	As per switch position
Baud Rate	19200
Serial Format	8N1

Configuration Settings

Default Mode

Default mode is useful when communication settings are unknown.

When the rotary address switch is set to 00:

• Server address = 1
• Baud rate = 19200
• Serial format = 8N1

Changing to default mode does not overwrite stored settings. Stored settings remain unchanged until written through Modbus.

Watchdog Action

The Bus Watchdog automatically resets all outputs to their initial safe state if communication with the Modbus client is lost. This helps ensure safe operation during cable disconnection, client failure, or other communication faults.

Configurable timeout: 1 to 600 seconds (100 ms resolution).

LED Indications and Diagnostics

LED	Description
Power	Module power ON indication
Tx	RS-485 transmit activity
Rx	RS-485 receive activity
X1–X24	Digital input status
Y1–Y24	Digital output status

Revision History

Revision	Date	Changes
Rev 1.0	2026-08-25	Initial Markdown datasheet

Get the latest version of this datasheet : click here..

Support

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Email: info@veawe.io