Advantages Of Rs232 Serial Communication

RS232 is a standard protocol used for serial communication, it is used for connecting computer and its peripheral devices to allow serial data exchange between them. As it obtains the voltage for the path used for the data exchange between the devices. It is used in serial communication up to 50 feet with the rate of 1.492kbps. RS232 Serial Link. You can connect the Microlink 3000 Series to the computer with an RS232 cable, and the Microlink 826 utility meter monitors.For logging data from instuments from other manufacturers we recommend the Windmill data acquisition software with the COMIML serial driver. Advantages of RS232.

A serial port is a communication interface over which serial communication can take place. On IBM compatible computers they are often referred to as COM ports. They allow external devices that transmit data serially to be connected to a host computer and allow two-way communication between the host and the device.Table of contents:.What is the RS232 protocol?or TIA/EIA-232 is a data transfer protocol designed to control serial communication.

It is used to organize the data flowing from a piece of Data Terminal Equipment (DTE) like a terminal or transmitter to a receiver or other type of Data Communications Equipment (DCE).The distance between the devices directly impacts communication speed. Serial communication can be established in either full-duplex or half-duplex mode. Full-duplex allows data to be sent and received simultaneously by using different wires for transmission and reception. In a half-duplex implementation, a single line is used for both transmitting and receiving data resulting in more limited operation. Half-duplex can be set to transmit or receive data, but not both at the same time. What is the RS485 protocol?The most widely used serial interface in industry is the or EIA-485 protocol. It has a major advantage over RS232 interfaces.

Through the use of multi-point topology, multiple receivers and transmitters can be connected. Data transmission is done using differential signals for more consistency.Two types of RS485 communication are possible:. RS485 interfaces with 2 contacts operate in half-duplex mode, either sending or receiving data exclusively at one time.

RS485 interfaces can also have 4 contacts in which case it can run in full-duplex mode. When used in this way data can be transmitted and received simultaneously.What is the difference between RS232 and RS485 serial ports?RS232 and RS485 are two standards for electrical transmission that was in existence before the introduction of personal computers. They are employed in interfaces that enable serial communication between computers and peripheral devices. While they both serve the purpose of allowing serial data transmission, the RS232 and RS485 protocols have some differences.

Let’s see where these protocols differ. The main difference between RS232 and RS485 serial ports are in:- Mode of operation - Communication distance - Voltage levels - The number of contacts in use, etc.So let’s take a look closer at these differences.The number of wires - An RS232 cable is typically comprised of 9 different wires, though in some connectors, 25 wires are used. Each wire serves a distinct purpose in the data transmission. RS485 cables only have three wires, 2 for data transmission and 1 for the ground.Two-way transmission - RS232 is full-duplex, meaning that it can transmit data in both directions, both sending and receiving. To achieve duplex communication with RS485 you need another set of wires. Native RS485 is half-duplex, meaning it can only transmit in one direction at a time.Voltage - RS485 uses voltages between +5V and -5V. The recommended voltage for RS232 is +12V to -12V, and signals degraded to as low as 3V can still be understood.

Range - There are significant differences in the cable lengths that can be used with the RS232 and RS485 protocols. RS232 cables are generally restricted to being 50 feet (15 m ) in length. Cables for RS485 can extend up to 4,000 feet (1,200 m).The differences in these two protocols can make one solution more favorable than the other in certain applications. The existence of RS232 to RS485 converters allow the two protocols to be used together. These converters usually work in both directions, allowing for both RS232 to RS485 and RS485 to RS232 connections. Where is the serial data transfer protocol used?Serial data transfer using the RS232 or RS485 protocols are no longer the standard for consumer computer or electronic peripheral devices, having been replaced by USB and other protocols.

Serial transmission is still used extensively in industrial monitoring and embedded systems and can be used with converters on USB equipped machines.RS232 allows direct control of industrial devices like UPS systems without the need for software assistance. Many industrial sensors and monitors employed in the Industrial Internet of Things make use of serial communication. It is also widely used with scientific and medical equipment. The RS485 protocol has found a widespread application in CCTV (Closed Circuit TV) cameras. Software technology used in serial communicationIf you work with serial interfaces and devices you may be in need of some software tools to assist you in carrying out your duties. Eltima software has developed three applications that make it easy to work with serial devices and extend their capabilities.

How to emulate a serial port in your system- This software utility allows you to create an unlimited number of virtual serial port pairs that emulate and behave as if they were physical COM ports. The tool does not use any of your real serial ports and can be used on machines that do not have any COM ports. Ports are recreated after a system reboot, and higher speed data transfer is possible through the virtual serial ports that when using physical ones.

These are just some of the features of this dedicated serial port software application. How to access remote RS232/485 serial device- If you have a need to access your remote serial devices over the network, this software application is a perfect solution.

It is designed to let you share an unlimited number of physical and virtual serial ports over any TCP/IP or UDP/IP network. You can create any number of virtual ports and name them in any way you like, and the networked serial ports can be used with virtual machines. It is a complete solution to the problem of controlling and accessing remote serial devices. How to monitor and analyze serial port activity- Here is a full-featured tool that has been developed to facilitate the monitoring of serial ports and is an indispensable tool for developers of serial applications. It enables you to track and analyze data flowing through all of your serial ports in one convenient log and allows you to look at the data in various display modes. You can monitor ports already opened by other applications, and emulate the sending of data to serial devices.

Among its other features is a playback option that lets you send the same data multiple times and will automatically compare the results and display differences. Eltima has extensive experience in the field of serial communication and these are mature software applications. If you work with serial devices and ports, you owe it to yourself to take a look at how you can benefit from these products. ConclusionsCommunication scenarios traveling over short distances that can tolerate low transmission speeds are best served by the RS232 protocol. It is simple and inexpensive to implement with readily available stock components such as UARTS, drivers, and connectors available for constructing the interface.

Data rates of 2 to 3 Mbits/s can be achieved for lines of limited length. Integrated circuits employing RS232 interfaces can make use of a single 3.3- or 5-V power supply with the inclusion of a charge pump and converter that supply positive and negative voltages.RS485 is better suited for high speed and long-range communication where the capability to implement duplex networking is desired. As with the RS232 interfaces, components are readily available for designing the interface.

The receivers and drivers in circuits enable more than 32 drops with data rates that can be as high as 40 Mbits/s. You can find ICs that support the RS485 protocol featuring converters to provide dual supply voltages.

RS-232 vs. TTL Serial Communication

Skill Level: Beginner

by jimblom November 23, 2010 15 comments

One of the tools we use most when debugging our projects is serial input/output. Serial is very easy to implement, and it allows you to send/receive any data you need from your microcontroller to a computer's serial port so it can be viewed using a terminal emulator. These two devices are compatible from a software perspective, however you can't just hook a microcontroller up to a computer because the hardware interfaces are not compatible.

Most microcontrollers these days have built in UARTs (universally asynchronous receiver/transmitter) that can be used to receive and transmit data serially. UARTs transmit one bit at a time at a specified data rate (i.e. 9600bps, 115200bps, etc.). This method of serial communication is sometimes referred to as TTL serial (transistor-transistor logic). Serial communication at a TTL level will always remain between the limits of 0V and Vcc, which is often 5V or 3.3V. A logic high ('1') is represented by Vcc, while a logic low ('0') is 0V.

The serial port on your computer (if it's lucky enough to have one, they're quickly becoming a relic) complies with the RS-232 (Recommended Standard 232) telecommunications standard. RS-232 signals are similar to your microcontroller's serial signals in that they transmit one bit at a time, at a specific baud rate, with or without parity and/or stop bits. The two differ solely at a hardware level. By the RS-232 standard a logic high ('1') is represented by a negative voltage – anywhere from -3 to -25V – while a logic low ('0') transmits a positive voltage that can be anywhere from +3 to +25V. On most PCs these signals swing from -13 to +13V.

The more extreme voltages of an RS-232 signal help to make it less susceptible to noise, interference, and degradation. This means that an RS-232 signal can generally travel longer physical distances than their TTL counterparts, while still providing a reliable data transmission.

This timing diagram shows both a TTL (bottom) and RS-232 signal sending 0b01010101

Solutions

So, you may see where the problem lies in interfacing these two signals. To connect these two ports you not only have to invert the signals, but you also have to deal with regulating the potentially harmful RS-232 voltages to something that won't destroy a microcontroller's serial pins. There are a handful of solutions to this problem of voltage converting and inverting. The most common, and easiest solution is just plugging a MAX-232 in between the two devices:

There are many generic derivatives of the MAX-232. Maxim IC just happened to be the first to market with this neato device (decades ago!) so out of habit, we call all ICs that do similar jobs 'MAX-232s'.

Less expensive solutions, like our RS-232 Shifter, use transistors or inverters to flip the signals, and charge pumps to get the voltages high enough to be RS-232 compliant:

Sample Question

With the above information at hand, here's a quick quiz to test your shiny new knowledge:

1. What are the two main differences between RS-232 and TTL signals?

2. True or false: Data is sent from a PC's RS-232 port at 9600 bits-per-second (bps), it's converted to TTL by a MAX232 before reaching a microcontroller. The voltages of the signals look different on each end, but the speed (bps) does not change.

Answers:

Spoiler Alert! Highlight from here..

1. The '1's and '0's are inverted from each other. The minimum and maximum voltages of RS-232 signals is +/-13V, and only 0 to 3.3V/5V for TTL signals.

2. True. The data rate will always remain the same, even if the voltages of the RS-232 and TTL signals are different.

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