What Are They, When to Use Them, and How to Choose
Don’t be scared — this isn’t a deep engineering article. We won’t dive into frame formats or explain how bits are transmitted under serial standards. Instead, this text will be informative enough to help you understand the idea behind serial protocols, their pros and cons, why RS-232/422/485 and Ethernet still co-exist today, and how all of this relates to MOXA NPort devices.
Prefer to skip the background on serial standards and MOXA NPort popularity? Jump straight to the practical part — our NPort Selection Guide.
Introduction: Serial protocols, COM-port, RS-232/422/485 in the nutshell
Let’s start with the basics: what is a serial protocol? In telecommunications and data transmission, serial communication is the process of sending data one bit at a time, sequentially, over a communication channel or computer bus. This is in contrast to parallel communication, where several bits are transmitted simultaneously over multiple parallel channels. Serial communication is mostly used when long-distance transmission is required, or when the cost and complexity of parallel wiring make parallel links impractical.
The most common serial communication standards are RS-232, RS-422, and RS-485. They cover only the first layer of the OSI model, are simple to understand and implement — yet reliable enough for industrial use. The RS family only defines how bits are transmitted: the electrical signals, the number of wires, and the voltage levels. Some revisions of the standards mention pinouts and connectors. But protocols, data structures, and all higher-level logic are left entirely up to the user. You can wrap it around Modbus RTU, proprietary protocols, or even just transmit raw data.
All three standards use a minimum of 2+1 wires (two data signals and ground), but some variations may use up to 8+1 (data signals, control signals, and ground). The number of wires depends on whether you need control signals or just pure data transmission.
Connector-wise, the most common is the DB9 type, often simply called a COM-port. However, in many industrial environments — such as automation cabinets — it’s often more convenient to use terminal blocks instead, which are easier to wire by hand. Fortunately, the RS standards are flexible enough to allow both.
Transmission distance and topology limitations:
- RS-232: up to 15 meters, strictly point-to-point.
- RS-422: up to 1200 meters, point-to-point support, allows for one driver and multiple receivers.
- RS-485: up to 1200 meters, point-to-point support, allows for true multipoint connections (multiple drivers and receivers on the same bus).
All three standards are relatively noise-immune:
- RS-232 uses a wide voltage range to differentiate signal from noise.
- RS-422 and RS-485 use differential signalling — sending inverted copies of the signal in parallel — to cancel out noise through phase inversion.
So, RS-232/422/485 use very simple and reliable technologies — and this exact simplicity made them so widespread in the 20th century that even today, no one has fully wiped them out from Operational Technology (OT) applications. RS-232 has been lasting for over 60 years, RS-422 for 50 years, and RS-485 for 40 years.
Serial application software is also much easier to develop compared to communication technologies like USB, Ethernet, or Wi-Fi. In many cases, a working serial communication program can be written in just a few lines of code, whereas USB or network applications may require thousands of lines and take days or even months to complete.
Given that industrial devices often run for 20-30+ years without replacement, every factory, substation, utility system, HVAC control, or POS terminal using RS-232/422/485 is helping to keep these ports alive. Sometimes, it feels like COM-ports are with us forever.
Serial-to-Ethernet: What is a Serial Device Server
Even though serial interfaces have proven themselves as amazingly reliable, they are clearly considered “legacy” today. Modern computers rarely come with COM-ports anymore, and by default, you can’t directly connect serial devices to network switches or Ethernet ports. The maximum speed of serial interfaces isn’t even close to 100 Mbps, and they don’t support modern technologies like redundancy protocols, SNMP monitoring, or direct cloud connectivity.
This situation brings us to a crossroads. On one hand, there are still millions of serial devices operating reliably across industries worldwide. On the other hand, the modern trend is unstoppable: everything is moving toward Cloud integration and Industrial IoT (IIoT) connectivity. This is exactly where Serial Device Servers come into play.
These are simple devices that have a serial port on one side and an Ethernet port on the other. Their main job is straightforward: to encapsulate serial data into IP packets (typically using TCP or UDP), allowing serial devices to join modern Ethernet networks. Some models are dedicated to a specific standard like RS-232, while others are universal, supporting RS-232/422/485 on the same device. They can be just palm-sized, or large rackmount units supporting up to 32 serial ports.
But the real strength of Serial Device Servers is not just in simple signal conversion. They offer a variety of operational modes that make integration easier without replacing legacy systems. For example, in Real COM mode, a special driver installed on a computer creates a virtual COM-port. From the software’s perspective, it still appears to be communicating with a local serial port — even though the actual communication is happening over Ethernet. Other modes include TCP Server, TCP Client, Pair Connection, Ethernet Modem, and it’s not even a full list.
Many modern models also add encryption and cybersecurity features to protect data in transit, meeting the demands of modern industrial networks.
Key Benefits of Connecting Serial Devices to Ethernet
Using Serial Device Servers brings a range of practical advantages:
- Cost savings: It’s much cheaper and faster to connect legacy devices through Serial Device Servers than to invest a huge amount of money all at once to replace everything in a single upgrade.
- Minimal downtime: Instead of shutting down operations to replace legacy hardware, you can modernize your infrastructure gradually, making the upgrade process almost seamless.
- Extended lifetime of legacy devices: If a device is still working reliably, there’s no reason to replace it. Serial Device Servers help you keep trusted equipment operating within modern networks, allowing you to build on what already works instead of throwing it away.
- Extended communication distance: RS-232 is limited to about 15 meters, and standard Ethernet over twisted-pair cable is limited to 100 meters. RS-485 can reach up to 1200 meters — but by converting to Ethernet over fiber optics, distances of dozens of kilometers become possible.
- Centralized control and monitoring: Once devices are Ethernet-enabled, they can be managed through SNMP, integrated into Network Management Software (NMS), and updated remotely with firmware patches and security updates.
At first glance, Serial Device Servers might seem like a temporary workaround between old and new technologies. However, looking at the bigger picture, it’s clear they are a critical long-term solution. The global RS-232/422/485 device market is still projected to grow at a CAGR of 5.76% through 2031, showing that millions of serial devices will continue operating for years to come. In this evolving world of connectivity, Serial Device Servers are essential bridges, helping industries navigate between proven technologies and future digital demands.
Why MOXA NPort is so popular? What makes it unique?
If you didn’t know yet, NPort is the product line of Serial Device Servers made by MOXA. Not only is NPort claimed to be the World’s #1 top-selling product in this category, but it is also one of the very first. Since its launch in 1998, NPort has been deployed in thousands of Industrial Automation projects worldwide. And as of the time of this writing, the number of Google searches including the word “NPort” exceeds 40,000 per month.
Why is that?
- Trusted Pioneer: As mentioned above, MOXA is one of the first Serial Device Server manufacturers in the world. It’s very hard to beat a trusted pioneer with more than 25 years of accumulated reputation.
- In-house Serial Technology: MOXA develops its own serial ASICs and drivers. This means they control the entire lifecycle of their NPort products — from hardware design to driver support — allowing them to continue production as long as the market requires it, and to quickly update drivers for all major operating systems.
- Cybersecurity Commitment: MOXA is committed to securing your serial device connections by offering serial-to-Ethernet solutions compliant with the latest IEC 62443-4-2 standards, along with ongoing security patch updates to stay ahead of new threats.
- Wide Operating System Support: MOXA’s NPort devices don’t just support Windows. They also offer driver support for a wide range of platforms, including OpenServer, QNX, Solaris 10, FreeBSD, AIX, HP-UX, and even Mac OS X.
- Rich Operation Modes: MOXA’s NPort supports a wide range of operational modes, including Real COM, RFC2217, TCP Server, TCP Client, UDP, Pair Connection, Ethernet Modem, and Reverse Telnet. It’s not easy to find another Serial Device Server with such a comprehensive feature set.
Add to these strengths the ease of use, well-known reliability built over 25 years, a 5-year warranty with long-term supply assurance, and seamless integration with MOXA’s MxView One network management platform — and you begin to understand where those 40,000 search requests per month come from.
How to choose your NPort - Starter Selection guide
Before we dive deep into every type of NPort product, let’s have a quick look at a simple table that can be your starting point:
Selection Guide for MOXA NPort Series
| NPort Type | NPort Series | Number of Serial Ports | Number of Ethernet Ports | Main Reason to Choose |
|---|---|---|---|---|
| General Device Servers | NPort 5000 NPort 5000A | 1, 2, 4, 8, 16 | 1 | All-round |
| Industrial Device Servers | NPort IA5000 NPort IA5000A NPort 5000AI-M12 | 1, 2, 4 | 1 or 2 | Maritime, Oil & Gas, and Transport certificates |
| Terminal Servers | NPort 6000 NPort 6000-G2 | 1, 2, 4, 8, 16, 32 | 1 + optional module (1 or 2) | Security features based on IEC 62443 |
| Combo Device Servers | NPort S8000 NPort S9000 | 4, 8, 16 | 4 or 5 | Ethernet Switch / Serial Device Server combo |
| Wireles Device Servers | NPort W2000A | 1 or 2 | 1 + Wi-Fi | IEEE 802.11 a/b/g/n Wi-Fi 4 solution |
Based on the “Main Reason to Choose” column above, you can scroll down to your preferred type, or simply read through all of them one by one to get the full picture.
Let’s go!
Types of NPort
Now that we know the main reasons to buy a Serial Device Server in general, MOXA NPorts specifically, and what key factors should be your starting point, let’s have a quick look at what types of NPorts exist — since the product range is quite vast.
General Device Servers
The most popular and commonly used type of NPorts is General Device Servers, which means they are not dedicated to any specific market or application — they simply do the job described above. You can see them everywhere: from supermarket cashier machines to industrial automation cabinets. In about 80% of cases, this is the most likely type of product you will need.
Selection Guide for MOXA General Device Servers:
| Series included |
Serial ports | Ethernet ports | Description | Security functions |
|---|---|---|---|---|
| NPort Express | 1 | 1 | Entry-level legacy NPort models with the basic yet most essential functions and metal housing – Only NPorts with female-type COM ports – Medical* certificates |
– |
| NPort 5100 | 1 | 1 | 1-port Classic NPorts covering most of the functions needed in mild environment – Cost effective – Highest MTBF among all General Device Servers |
Local database (password only) |
| NPort 5200 | 2 | 1 | 2-port Classic NPorts covering most of the functions needed in mild environment – Models with ‘I’ suffix have 2 kV isolation on serial ports – DNV* and Medical* certificates |
Local Database |
| NPort 5100A | 1 | 1 | 1-port Advanced NPorts covering most functions required in mild environments – Better surge protection than Classic models |
Local Database Encryption HTTPS |
| NPort 5200A | 2 | 1 | 2-port Advanced NPorts covering most functions required in mild environments – Better surge protection than Classic models – Dual DC power inputs |
Local Database Encryption HTTPS |
| NPort P5150A | 1 | 1 (PoE) | PoE-enabled Advanced NPort covering most functions required in mild environments – Only NPort supporting PoE (IEEE 802.3af) – Supports both power adapter and PoE – Better surge protection than Classic models |
Local Database Encryption |
| NPort 5400 | 4 | 1 | Classic NPorts with 2 or 4 ports covering most of the functions needed in mild environment – User-friendly LCD panel and configuration buttons – Dual DC Power Inputs – Models with *I have 2kV isolation of serial ports – DNV and Medical* certificates |
Local Database Encryption HTTPS SNMPv3 |
| NPort 5600 | 8 or 16 | 1 | Multi-port rackmount NPorts with wide power input options – Rackmount design – RJ45, multi-mode SC, or single-mode SC Ethernet options – All serial ports use RJ45 connectors – Supports 48 VDC, HVDC, and VAC inputs – Highest surge protection among all General Device Servers – Medical* certificates |
Local Database Encryption HTTPS SNMPv3 |
| NPort 5600-DT | 8 or 16 | 2 | Compact desktop version of the 5600 series with 2 Ethernet ports – 2 Ethernet Ports for Convenient Cascade Wiring – Dual power inputs – Table box design |
Local Database Encryption HTTPS SNMPv3 |
| * Not all models in the series | ||||
Industrial Device Servers
Industrial Device Servers are types of NPorts designed specifically for industrial automation use. They are available in two form factors: DIN-rail mount for automation cabinets, and flat designs with screw holes for wall mounting (or DIN-rail mount with an adapter).
DIN-rail models are C1D2, ATEX, and IECEx certified for hazardous industrial environments, while flat models are EN 50121-4 compliant, pass EN 50155 mandatory tests, and feature M12 Ethernet ports. If you need compliance with industrial standards, or DIN-rail/wall-mount design is critical, Industrial Device Servers are your choice.
DIN-rail models have two Ethernet ports for cascading without requiring an external switch. Flat models have one Ethernet port, but offer an M12 connector for enhanced vibration resistance.
The number of serial ports available is 1, 2, or 4 — all models are universal RS-232/422/485.
Industrial Device Servers include:
- NPort IA5000
- NPort IA5000A
- NPort 5000AI-M12
Terminal Servers
Terminal Servers are the right choice when cybersecurity is your #1 priority. They offer additional encryption options and secure operation modes for Real COM, TCP Server, TCP Client, Pair Connection, Terminal, and Reverse Terminal. MOXA’s Terminal Servers are built following the IEC 62443-4-2 design guidelines to securely connect terminals, modems, data switches, mainframes, and POS devices to networks.
The number of serial ports can be 1, 2, 4, 8, 16, or 32. Depending on the model, serial ports may be COM-ports (DB9) or RJ-45 connectors. Some models are RS-232 only; others are universal RS-232/422/485. Form factors vary from compact palm-sized devices to full rackmount units.
All MOXA Terminal Servers support authentication via Local database, RADIUS, and TACACS+. They also support encryption protocols like HTTPS, AES, SHA, and security protocols such as HTTPS (TLS 1.2), SNMPv3, and SSH. Rackmount models additionally support Layer 2 Ethernet redundancy (STP/RSTP/Turbo Ring), while all models support Layer 3 features like RIP v1/v2 and Static Routing.
The most advanced cybersecurity features, such as Secure Boot (which ensures only Moxa-authorized firmware runs), are offered in the 2nd-generation Terminal Servers.
Terminal Servers include:
- NPort 6100
- Nport 6200
- NPort 6100-G2
- NPort 6200-G2
- NPort 6400
- NPort 6600
Note: beside NPorts, MOXA Terminal servers are also presented in CN-series, which are not covered by this article.
Combo Device Servers
MOXA’s Combo Device Servers offer a unique combination of two worlds: Serial Device Servers and Industrial Ethernet Switches.
In simple terms, they are MOXA-managed switches with integrated serial ports. The aim of this product line is to satisfy complex project requirements, reduce the space needed for separate devices, and simplify configuration and maintenance.
In one box, you get:
- From the switch side: Ethernet redundancy protocols like Turbo Ring, Turbo Chain, and RSTP/STP.
- From the Serial Device Server side: classic NPort modes like Real COM, RFC2217, TCP Server, TCP Client, and UDP.
Combo Device Servers are designed for industrial use — supporting IEC 61850 MMS, C1D2 certification, and EMI/EMS certifications.
Form factors are DIN-rail or rackmount, depending on the model. Ethernet ports: 4 or 5. Serial ports: 4, 8, or 16.
MOXA Combo Device Servers include:
- NPort S8000
- NPort S9450I
- NPort S9650I
Wireless Device Servers
Wireless Device Servers is the last NPort type in the list, and it’s quite unique. Instead of converting serial signals into Ethernet packets, these devices transmit serial data via Wi-Fi (as Wi-Fi clients). At the same time, they still include an Ethernet port — giving you dual connection options. However, you need to configure LAN and WLAN settings carefully, as there are different ways to handle them together.
The basic serial functionality is similar to General Device Servers. All models have 1 or 2 serial ports, supporting universal RS-232/422/485 communication.
MOXA Wireless Device Servers include:
- NPort W2150A-W4
- NPort W2250A-W4
Reasons to purchase NPort from APulsar in Malaysia
Now that you understand why MOXA Serial Device Servers are so good, and how to choose the right one for your project, only one question remains: why should you buy NPorts from APulsar?
Here are our top 9 reasons:
- Official MOXA Distributor: APulsar is an official authorized distributor of MOXA products. You can check our status here. On top of that, APulsar is the largest MOXA distributor in Malaysia.
- Certified Expertise: APulsar holds MOXA’s official certifications — MXCA (MOXA Certified Associate Trainer) and MTSC (MOXA Technical Support Certification). MXCA certifies our ability to deliver technical training on MOXA products, while MTSC proves our deep knowledge of MOXA’s latest products and technologies.
- Unmatched Experience: Across our team, we share over 50 years of combined experience working with MOXA products, and NPort devices specifically. Some of our engineers have worked with MOXA Serial Device Servers for more than 10 or even 20 years.
- Ready Stock Availability: We keep the most popular NPort models — especially 1-port and 2-port General Device Servers — in stock. Just send us your request!
- Instant Delivery: If the model you need is in stock, we can ship it to you the same day anywhere in Malaysia. If you are based in Kuala Lumpur, you are welcome to visit our office in Petaling Jaya, pay via cash or Touch ’n Go, and receive your NPort within hours!
- Fast Shipment from Taiwan: If the model you need is not in stock, we can typically deliver it within 1–2 weeks directly from MOXA’s facilities.
- Test Drive Available: Want to try before you buy? You can take any in-stock NPort model for a free test drive.
- Post-Sales Support: We never leave you alone after your purchase. When you buy from APulsar, you receive lifetime free online technical support for your NPort. If needed, we also offer on-site technical support provided by our experienced engineers as an additional service. Whenever you need help, just send us a message or give us a call.
- Personalized Selection Assistance: Struggling to navigate the huge range of products? We are here to help! Just call or message us, tell us a little about your project, and our specialists will quickly help you choose the right NPort for your specific needs.
Final Words
The APulsar team hopes that this article has been insightful for you. Anytime you need advice, assistance, or technical support — just contact us.
And if you would like to see more useful guides like this one, don’t forget to subscribe to our newsletter below!
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