Milestone Electronics
RS232 to 4 RS422/RS485 Convertor Distributor
The LD-104UDP converts a single RS232 input into four independent RS422/RS485 outputs, enabling high-speed data distribution over long distances of up to 1.2 km under high-noise industrial conditions. Each output is individually opto-isolated and spike-suppressed for reliable, interference-free operation.
- 1 composite AV input distributed to 4 independent AV outputs
- Audio and video signals transmitted together without delay or mismatch
- Each output individually managed and amplified for consistent signal strength
- Video bandwidth up to 90 MHz (-3dB) with 75-ohm impedance matching
- Rugged metal enclosure with captive screw audio connectors for fixed installations
Max Resolution
1080p Full HD
Audio Input
Stereo Analogue
Output
Single HDMI
- In-house manufactured
- 24hr response
- 2,000+ clients served
Product Overview
What the LD-104UDP delivers
The LD-104UDP is a RS232 to RS422/RS485 Convertor Distributor designed for high-speed data transmission between computer systems and peripheral devices over long distances under high-noise industrial conditions. It accepts a single RS232 input and simultaneously distributes the signal to four independent RS422/RS485 outputs, each connected via a 3-pin Phonex connector.
Each output line provides a dual-line interface per signal, with individual opto-isolation and spike suppression built in. The transient protection rating of 2500 V peak ensures the unit can reliably operate in electrically noisy environments such as factory floors, control panels, and industrial automation systems without signal degradation or equipment damage.
The RS232 input is connected via a 3-pin Phonex connector accepting TxD, RxD, and GND signals from the host computer COM port. Output wiring follows a standard twisted pair cable arrangement with a maximum cable resistance of 90 ohms per 1000 metres, and the unit supports transmission distances of up to 1.2 km at 19,200 bps.
A built-in 230V mains power supply rated at up to 50 VA powers the unit directly from a standard AC mains socket. Front panel LED indicators for Power, Tx, Rx1, Rx2, Rx3, and Rx4 allow real-time monitoring of signal activity across all active lines during operation.
Input
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Key Features
Built for industrial-grade serial data distribution
The LD-104UDP combines long-range RS422/RS485 signal distribution with per-port isolation and high transient protection, making it suitable for demanding industrial communication environments.
1 RS232 Input to 4 RS422/RS485 Outputs
A single RS232 input from a host computer COM port is converted and distributed simultaneously to four independent RS422/RS485 output ports. Each output is individually accessible via a 3-pin Phonex connector carrying the standard -Tx/Rx(A), GRD, and +Tx/Rx(B) signals.
- RS232 input: TxD, RxD, GND on 3-pin Phonex connector
- 4 independent RS422/RS485 outputs with individual connectors
- Dual-line interface per signal for high common mode noise rejection
Long-Distance Transmission up to 1.2 Km
The RS422/RS485 differential signal standard allows data transmission over distances of up to 1.2 km at 19,200 bps. This makes the LD-104UDP suitable for applications where remote terminals, controllers, or peripherals are installed at significant distances from the host computer system.
- Maximum transmission distance: 1.2 Km at 19,200 bps
- Designed for use with twisted pair shielded cable, 90 ohms per km maximum
- Cable must be run through conduit pipe for physical protection
Per-Output Opto-Isolation and Spike Suppression
Each RS422/RS485 output is individually protected by an opto-isolator and spike suppressor. This ensures that electrical noise, ground loops, or voltage spikes on connected field devices do not propagate back into the host computer or affect other output channels.
- Opto-isolation on every output channel
- Spike suppressor on every output channel
- Transient protection rated at 2500 V peak
Front Panel LED Status Indicators
The front panel includes dedicated LED indicators for Power, Tx, Rx1, Rx2, Rx3, and Rx4. These allow operators to visually confirm power status and monitor real-time data activity across each of the four output channels without requiring external test equipment.
- Separate indicators for Tx and each Rx output line
- Power LED confirms unit is energised and operational
- Enables quick fault identification during commissioning and maintenance
Built-In 230V Mains Power Supply
The unit includes a self-contained power supply that operates directly from a 230V, 50 Hz mains supply, rated up to 50 VA. No external power adapter or separate supply unit is required, simplifying installation and reducing the number of components needed in the field.
- Mains input: 230V, 50 Hz
- Built-in supply rated up to 50 VA
- No external power adapter required
High Common Mode Noise Rejection
The RS422/RS485 outputs use a balanced differential signalling architecture where each signal pair carries both the positive and negative signal lines. When laid using a twisted pair cable, this configuration provides high common mode noise rejection, making the LD-104UDP well suited to electrically noisy factory and industrial environments.
- Differential signal pair per channel for noise immunity
- Compatible with twisted pair shielded cable
- Cabling must not be run parallel to power line cables
Installation
Connecting the LD-104UDP to your system
The LD-104UDP connects to a standard PC COM port via RS232 and distributes the signal to up to four RS422/RS485 field devices over twisted pair cabling. Follow the port pinouts and cable-laying guidelines below for a correct installation.
01
RS232 Input Wiring
Connect the host computer COM port to the RS232 input using a 3-pin Phonex connector. For a standard PC COM port (D-25F or D-9F), wire pin 2 (Tx) on D-25F or pin 3 on D-9F to pin 2 (Rx In) on the Phonex connector. Wire pin 3 (Rx) on D-25F or pin 2 on D-9F to pin 1 (Tx Out). Wire pin 7 (GND) on D-25F or pin 5 on D-9F to pin 3 (Signal Ground). Verify connections for any non-standard terminal before making the cable.
02
RS422/RS485 Output Wiring and Cable Laying
Each output port uses a 3-pin Phonex connector. Pin 1 carries -Tx/Rx (A), Pin 2 is GRD, and Pin 3 carries +Tx/Rx (B). Use a twisted pair shielded cable with maximum resistance of 90 ohms per 1000 metres. Do not lay this cable parallel to power line cables. Run the cable through a conduit pipe for physical protection. For RS485 configurations, fit a 180-ohm terminating resistor at each end between the + and - output terminals.
Where the LD-104UDP performs
Designed for industrial and commercial environments where a single host computer must communicate with multiple remote serial devices over long distances under electrically noisy conditions.
Factory Automation
Connect a single host control computer to multiple RS485-compatible automation devices across a factory floor. The long transmission range and noise rejection capabilities are well matched to the electrical environment of production facilities.
Programmable Logic Controllers
Interface a supervisory computer with up to four PLCs using RS422/RS485 communication links. The individual opto-isolation on each output ensures that faults or voltage irregularities on one PLC connection do not affect other channels or the host system.
Attendance Recording Systems
Distribute RS232 data from a central attendance management server to multiple terminal units installed across different locations in a building or campus. The four-output distribution removes the need for separate convertor hardware at each terminal point.
Barcode Readers
Connect multiple barcode scanners on RS422/RS485 links back to a single host system for centralised data capture and processing. Suitable for warehouse, retail, and logistics environments where several scanning stations feed into one system.
Remote Data Transmission
Transmit serial data from a central computer system to remote terminals or data collection points located up to 1.2 km away. The balanced differential signalling ensures data integrity even where long cable runs pass through areas with significant electromagnetic interference.
EPABX Systems
Provide RS422/RS485 serial communication links between a central EPABX controller and remote extension modules or management terminals distributed across a facility. The high transient protection and noise immunity suit the mixed electrical environment of telephone and data infrastructure.
Full specification sheet
- Input
- Outputs
- Signal Performance
- Front Panel Indicators
- Power
- RS232 Port Wiring Reference (Standard PC COM Port)
FAQs about the LD-104UDP
What does the LD-104UDP do?
The LD-104UDP is a RS232 to RS422/RS485 Convertor Distributor. It accepts a single RS232 input from a host computer and simultaneously distributes the converted signal to four independent RS422/RS485 output ports. This allows one computer COM port to communicate with up to four RS485-compatible field devices over long-distance twisted pair cabling in a single installation.
What is the maximum cable distance supported?
The LD-104UDP supports a maximum transmission distance of 1.2 km at a data rate of 19,200 bps. The output cabling must be a twisted pair shielded cable with a maximum resistance of 90 ohms per 1000 metres. Cables should be routed through a conduit pipe for physical protection and must not be laid parallel to power line cables to avoid interference.
Is each output independently isolated from the others?
Yes. Each RS422/RS485 output has its own individual opto-isolator and spike suppressor. This means that a fault condition, ground loop, or voltage spike on one connected device will not propagate to other output channels or back into the host computer. The transient protection is rated at 2500 V peak across all outputs.
What type of connector is used for the RS232 input and RS485 outputs?
Both the RS232 input and all RS422/RS485 outputs use 3-pin Phonex connectors. The RS232 input carries TxD on pin 1, RxD on pin 2, and Signal Ground on pin 3. Each RS422/RS485 output carries -Tx/Rx (A) on pin 1, GRD on pin 2, and +Tx/Rx (B) on pin 3. A wiring reference table for standard PC COM ports in D-25F and D-9F configurations is provided in the product manual.
Does the LD-104UDP need an external power supply?
No. The LD-104UDP includes a built-in power supply that operates directly from a 230V, 50 Hz mains input, rated up to 50 VA. No separate external power adapter or auxiliary supply is required. Once connected to a standard AC mains socket, the unit is ready for operation as indicated by the front panel Power LED.
Is a terminating resistor required for RS485 wiring?
Yes. For RS485 configurations, a terminating resistor of 180 ohms is required at each end of the cable, connected between the + and – output terminals of the RS485 port. This termination is necessary to prevent signal reflections on the transmission line, particularly at the data rates and distances involved in industrial RS485 installations.
Can the LD-104UDP be used if my computer COM port uses a D-9 or D-25 connector instead of Phonex?
Yes. The RS232 input of the LD-104UDP uses a 3-pin Phonex connector, so an adapter cable is required to connect from the computer’s D-9F or D-25F COM port. The product manual provides a pin-by-pin wiring table covering both D-25F and D-9F PC COM port configurations, mapping each signal to the correct pin on the Phonex connector. If your terminal is non-standard, verify the wiring against your device documentation before making the cable.
What happens to the other output channels if one connected device develops a fault?
Because each of the four RS422/RS485 outputs has its own independent opto-isolation and spike suppression circuit, a fault on one output channel is isolated from the remaining channels. A wiring fault, ground potential difference, or transient voltage on one field device will not affect the signal integrity or hardware on the other three output ports or on the RS232 input side connected to the host computer.
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