RS232 vs RS485 – What are their differences?

RS232 vs RS485. Both serial communication standards made major impacts on the industry. They are still both fairly widely used even though they are introduced more than half a century ago. They are two not very different serial communicators. In the industry, their application varies by not a lot.

Before we continue, you may check out our other articles to learn more about the RS232 and RS485 respectively.

• What is RS232 and How to get started
• All about RS485 – How RS485 Works and How to Implement RS485 into Industrial Control Systems?

Both RS232 and RS485 can be found in applications such as:

• Scientific equipment
• Industrial wireless controls
• Computers
• Robots
• Medical equipment, etc.

Main Differences

Therefore, how do we choose between RS232 and RS485? For this, we shall dive into their main differences:

1. Operational Distance
2. Immunity to Electrical Noise and Ground Potential
3. No. of Transmitters and Receivers
4. Data Transmission Speed

SPECIFICATIONS

	RS232	RS485
Voltage System	Voltage level-based	Differential
Total Drivers and Receivers on One Line	1 Driver, 1 Receiver	32 Drivers, 32 Receivers(One Driver active at a time)
Line Configuration	Point-to-point	Multidrop
Maximum Operational Distance	15M / 50FT	1,200M / 3000FT
Maximum Data Transmission Rate	1MBit/s	10MBit/s
Duplex Mode	Full Duplex	Half Duplex or Full Duplex
Maximum Driver Output Voltage	+/-25V	-7V to +12V
Receiver Input Resistance	3 to 7 kΩ	12 kΩ
Receiver Input Voltage Range	+/-15V	-7V to +12V
Receiver Sensitivity	+/-3V	±200mV

Operational Distance

The maximum operational distance between a transmitter and a receiver for RS232 is 15 Meters. However, the length can be extended considerably with a trade-off with slower data rates. 

For RS485, the distance is remarkably longers of up to 1200 Meters. That’s 24 times the distance of RS232. It will only be reasonable to pick RS485 if the equipment is meant to operate at a distance from the transmitter.

Immunity to Electrical Noise and Ground Potential

RS232 operates on a voltage level-based system that performs well when differences in ground potential are minimal. However, in electrically noisy environments with different potential levels, RS232 is too fragile and allows data corruption.

In contrast, RS485 operates on a differential voltage system. This allows RS485 to demonstrate higher levels of noise immunity. The differential voltage system also allows the RS485 to provide longer data transfer distance and lower voltage use, which helps to increase data speed.

No. of Transmitters and Receivers

An RS232 Serial Interface is for connecting two devices. There will be one transmitter and one receiver. An RS485 Serial interface can connect up to 32 devices to a single transmitter.

Do also take note that RS232 and RS485 are not fixed. Newer equipment uses a USB interface more commonly. Therefore, making different kinds of equipment or older and newer devices work together requires a conversion from USB to RS232 or RS485 or RS485 or RS232 to USB. It may also be necessary to convert RS232 to RS485 or vice-versa.

Converters are readily available for these purposes. Here are a few.

USB TO RS232 / RS485 / TTL Industrial Isolated Converter

• This converter converts a USB port to not only RS485 but also RS232 and TTL, making it more versatile.
• It also features embedded circuits protection features such as power isolation, ADI magnetical isolation, and TVS diode.
• It is built to last with its aluminium alloy enclosure.
• It is unquestionably an ideal choice for industrial equipment use due to its high speed, reliability, safety and versatility.

Industrial USB to RS485 Converter

• Clueing in from its name, this is a USB to RS485 converter with industrial-grade features. 
• It converts a USB port to use with RS485.
• Best known for the simplicity of usage it provides, it also features embedded circuits protection features such as lightning-proofing, resettable fuse, ESD protection and TVS diode. 
• It allows for automatic transceiving, providing convenience.
• It is also an ideal choice for industrial equipment use due to its high speed, reliability and safety.

Other RS232 and RS485 Devices

RS232 Shield

• This RS232 Shield is based on the MAX232, a dual driver/receiver with a capacitive voltage generator that can supply TIA/EIA-232-F voltage levels from a single 5-V supply.
• The shield includes female DB9 connectors for connecting to a variety of RS232-compatible devices.
• On unused space, there are welding areas implemented for the added convenience while prototyping!
• This shield will be ideal for connecting your Arduino to any RS232 devices, and it is also stackable for multiple serial I/O ports!

SenseCAP Industrial-grade 4G Data Logger with MODBUS-RTU RS485 protocol

• This is an Industrial-grade 4G Data Logger from the Seeed’s SenseCAP product series.
• It can connect up to 32 RS-485 sensors, designed industry standard. 
• It is IP66 rated, waterproof and dustproof, which makes it ideal for long-term remote environmental monitoring in indoor and outdoor severe environments.
• The data collected can be sent to your server via cellular 2G/3G/4G!
• It comes in two versions, one with DC only, and another with a built-in rechargeable battery.
• This is a complete data logger for your Industrial IoT needs!

SenseCAP is a wireless sensing platform developed specifically for Industrial IoT, with applications in smart agriculture, smart cities, and other environmental sensing scenarios. It is made up of hardware products (sensors, data loggers, and gateways, for example), software services (SenseCAP portal, mobile App, open dashboard), and an API for system and data management. SenseCAP is compatible with a variety of communication protocols, including LoRa, 2G, 4G, NB-IoT, and more. Find out more here!

Industrial EC & TDS Sensor B MODBUS-RTU RS485

• Here’s an example of a SenseCAP RS485 sensor! This is a sensor that can collect data for Electrical Conductivity (EC) and Total Dissolved Solids (TDS) in Liquids.
• It comes with temperature compensation to compensate for the temperature changes for a more precise reading.
• Designed with industry standards, it comes with a waterproof aviation connector to ensure that your connection will not be affected by the elements.
• It is designed with RS485 built-in to be connected to the above data logger, where the data will wirelessly transmit to the cloud. 
• There is a whole plethora of SenseCAP industrial-grade sensor, and this is just one of the many! Find out more here!

Data Transmission Speed

RS232 is more than able to perform for a short distance and low data speed requirements. RS232 has a transmission speed of 1Mb/s up to 15M. However, RS485 has a data transmission speed of up to 10Mb/s for a distance of 15M. At the maximum of 1200M, RS485 transmits at 100Kb/s.

Real-World Applications

RS232 original purpose is to interconnect a terminal with a modem. However, it was used beyond its original purpose over the years. Most personal computers had RS232 compatible serial ports. It was used to connect peripherals such as keyboards, mice, and printers to the computers. However, most RS232 ports have been replaced in personal computers by USB today. This is due to USBs’ advantages of being faster, having lower voltages, and having connectors that are simple to connect and use.

However, RS232 are still being used today as they are far more immune to electromagnetic interference. RS232 also has a longer maximum cable length (15 Meters for RS232 vs 5 Meters for USB). Most older devices also only support RS232. RS232 is also used for laboratory automation surveying. RS232 is used to program PLCs, servo drives, variable-frequency drives, and computerized numerical control equipment.

RS485 is used in many computer and automation systems. Some of the examples are robotics, base stations, motor drives, video surveillance and also home appliances. In computer systems, RS485 is used for data transmission between the controller and a disk drive. Commercial aircraft cabins’ also use RS485 for low-speed data communications. This is due to the minimal wiring required due to the wiring configuration requirements of RS485. 

RS485 is however most popularly used in programmable logic controllers and factory floors where there is lots of electrical noise. RS485 is used as the physical layer for many standards and proprietary automation protocols to implement control systems, most commonly Modbus and Profibus. 

RS485 is also used in performance venues to control lights and systems such as the one shown below. 

Ref: Harman

RS485 are also commonly used for building automation as the simple wiring configuration and lengthy cable length is ideal for joining remote devices. It is commonly implemented to control video surveillance systems and link security control panels to devices such as access control card readers.

Learn more about Seeed’s IIoT

Here at Seeed, we believe that the Internet-of-Things (IoT) will be a new class of digital and physical infrastructures that will allow a more intelligent society. The cornerstone of this complex system is a dependable physical sensing network!

With best-in-class IIoT solutions constructed with premium products and services, Seeed aims to serve smart agriculture, smart weather stations, smart cities, and other environmental-sensing scenarios.

Our range of IIoT products is wide, with different sensors and hubs for different scenarios and requirements. Find out more about our different IIoT product solutions here!

In a nutshell,

If you’re looking for a low data transmission speed over a short distance, the RS232 will suffice, even though it is slightly archaic. The RS232 will be less expensive and simpler to integrate as compared to RS485. However, if you require a higher data transfer speed over a longer distance, RS485 will work better. If you need to control multiple devices, the RS485 will be a better pick as well. 

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