8 DO
Compact Modbus RTU remote I/O module with eight digital NPN outputs and configurable ON/OFF delay control.
Key Features
- 8 Digital NPN Outputs
- 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 mountable
- Dimensions: 110 mm × 50 mm × 55 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-8DO | 8-Channel Digital Output Modbus Remote I/O Module |
| UIO-8DI | 8-Channel Digital Input Modbus Remote I/O Module |
| UIO-4DI-4DO | 4-Channel Digital Input / 4-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-24DO | 24-Channel Digital Input / 24-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 |
Applications
- Driving relays, solenoids, and indicator lamps from a single compact Modbus module
- Adding 8 channels of NPN output expansion to PLCs and SCADA systems in space-constrained panels
- Replacing traditional timer relays with software-configurable ON/OFF delay logic on each output channel
- Sequencing or staggering equipment start-up using per-channel output delay
Specifications
| Parameter | Value |
|---|---|
| Mounting | DIN rail mountable |
| Dimensions | 110 mm × 50 mm × 55 mm (L × W × H) |
Electrical Specifications
| Parameter | Value |
|---|---|
| Supply Voltage | 15–24V DC |
| Digital Output Rating | 24VDC 500mA max, NPN Control |
| Communication Port | RS-485 |
Input/Output Specifications
| Parameter | Value |
|---|---|
| Digital Output Channel Count | 8 |
| Output Type | Digital NPN |
| 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 |
|---|---|---|---|
| Signal | A | B | Shield |
Bottom Connector – Power
| Pin | 1 | 2 |
|---|---|---|
| Signal | 24V | GND |
Digital Output Connector
| Pin | 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 |
|---|---|---|---|---|---|---|---|---|
| Signal | Y1 | Y2 | Y3 | Y4 | Y5 | Y6 | Y7 | Y8 |
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 |
|---|---|---|---|
| DO1–DO8 | 00001–00008 | Bit | DO1 to DO8 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 |
|---|---|---|---|
| Coils | 00001–00008 | Bit | DO1 to DO8 digital output control and status |
| Coils | 00401–00408 | Bit | Pending DO1 to DO8 delay status and override |
| Holding Registers | 40401–40408 | int16 | DO1 to DO8 ON delay |
| Holding Registers | 40451–40458 | int16 | DO1 to DO8 OFF delay |
| Holding Registers | 40501–40503 | int16 | HSO1 to HSO3 mode |
| Holding Registers | 40511–40516 | int32 | HSO1 to HSO3 freq |
| Holding Registers | 40531–40533 | int16 | HSO1 to HSO3 duty |
| Holding Registers | 40101 | int16 | Modbus server (slave) address |
Detailed Register Tables
Coils (0xxxx)
Digital Output Control
| Address | Type | Description |
|---|---|---|
| 00001–00008 | Bit | DO1 to DO8 digital output control and status |
Pending Output State
| Address | Type | Description |
|---|---|---|
| 00401–00408 | Bit | Pending DO1 to DO8 state while ON/OFF delay timer is active |
Writing 1 to a pending coil overrides the delay timer and immediately switches the output ON.
Holding Registers (4xxxx)
Digital Output Delay Configuration
| Address | Type | Description |
|---|---|---|
| 40401–40408 | int16 | DO1 to DO8 ON delay |
| 40451–40458 | int16 | DO1 to DO8 OFF delay |
Delay Resolution: 1 = 10 ms, 100 = 1 second. Maximum value: 65535 = 655.35 seconds.
High Speed Output Configuration
| Address | Type | Description |
|---|---|---|
| 40501–40503 | int16 | Y5, Y6, Y7 (HSO) mode. 0 = Digital output (master controlled), 1 = PWM continuous, 2 = PWM controlled |
| 40511–40516 | int32 | Y5, Y6, Y7 (HSO) PWM frequency, 0–20000 Hz |
| 40531–40533 | int16 | Y5, Y6, Y7 (HSO) PWM duty %, 0–100.0% (raw 0–1000) |
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 |
| Y1–Y8 | Digital output status |
Revision History
| Revision | Date | Changes |
|---|---|---|
| Rev 1.0 | 2026-08-25 | Initial datasheet, HW Version = 3, FW Version = 2 |
Get the latest version of this datasheet : click here..
Support
Website: www.veawe.io
Email: info@veawe.io