INTRODUCTION TO COMPUTER INTERFACES

RS232RS422

RS485

SERIAL PORT

It is a serial communication physical

interface through which information

transfers in or out one bit at a time.

Serial ports are still used in these

areas as they are simple, cheap and their

console functions are highly standardized

and widespread.

Throughout most of the history of 

personal computers, data transfer through

serial ports connected the computer to

devices such as terminals and various

peripherals.

RS232

The oldest and best known standard is 

RS-232 is definitely the most popular interface,

also being one of the first and is widely used

because it is so readily available. RS-

232 (Recommended Standard 232) is the

traditional name for a series of standards for 

serial binary single-ended data and control

 signals connecting between a DTE (

Data Terminal Equipment) and a DCE (

Data Circuit-terminating Equipment). It is

commonly used in computer serial ports.

RS232-9-pinout

RS232-9P-Female-to-9P-Female-13224750865

RS232RS-232 was first introduced in

1962. The original DTEs were electromechanical teletypewriters, and the original DCEs were (usually) modems. RS-232-compatible port was a standard feature for serial communications, such as modem connections. It is relatively short distances and low speed the RS232 serial interface

USB-To-RS232-Cable-YH-USB-RS232B-

usb-to-serial-rs232-adapter-1004462727

RS232RS232 was specifically defined as an

interface between computers, printers and terminals with modems. The modem would translate the communication signals to protocol usable for long distance communication, where long distance could also mean a device on the other side of the control room or building.

Furthermore, the RS232 linedriver is only designed to serve one receiver.

RS232-Cable

USB-RS232-Serial-Cable-Adapter

RS232RS-232 is still used to connect older

designs of peripherals, industrial equipment (such as PLCs), console ports, and special purpose equipment, such as a cash drawer for a cash register. An RS-232 serial port can communicate to some embedded systems such as routers as an alternative to network mode of monitoring. An RS-232 port was once a standard feature of a personal computer for connections to modems, printers, mice, data storage, un-interruptible power supplies, and other peripheral devices.

rs232-DB25-DB9

RS232 DB9 Serial to RJ45 Cat5 Ethernet Adapter Cable

RS232’s disadvantages

1. Limited Distance - Cable lengths are limited to 50 ft or less. Many will claim to go further, but this is not recommended, and is not part of the RS-232 specification.

2. Susceptible to Noise - RS-232 is single-ended, which means that the transmit and receive lines are referenced to a common ground

disadvantages

3. Not Multi-drop - You can only

connect one RS-232 device per port.

There are some devices designed to

echo a command to a second unit of

the same family of products, but this

is very rare. This means that if you

have 3 meters to connect to a PC,

you will need 3 ports, or at least, an

RS-232 multiplexor.

RS422It is a technical standard that

specifies electrical characteristics of a digital signaling circuit. Differential-mode signals can be sent at rates as high as 10 million bits per second, or may be sent on cables as long as 1200 meters.

It is a telecommunications standard for binary serial communications between devices. It is the protocol or specifications that must be followed to allow two devices that implement this standard to speak to each other.

RS422

RS422

RS 422 is the common short form title of American National Standards Institute (ANSI) standard  ANSI/TIA/EIA-422-B Electrical Characteristics of Balanced Voltage Differential Interface Circuits.

RS-422 is an updated version of the original serial protocol known as RS-232.

OPTO-RS422-pinoutusb-rs422

RS422Serial, balanced and differential are

the keywords for the RS422 interface standard. Serial means that the information is sent bit by bit on a single transmission line, just like with RS232. Balanced differential is what makes RS422 different from RS232. On RS232 interfaces, the signals are send on lines which share a common zero. With RS422, each signal line consists of two wires, preferably twisted to reduce noise.

RS232 and RS422Pin out

RS422

RS422 allows the direct connection of intelligent devices, without the need of modems and a RS422 linedriver can serve up to ten receivers in parallel. It is a balanced four wire system. The signal sent from the DTE device is transmitted to the DCE device through two wires and the signal sent from the DEC device to the DTE device is transmitted through the other two wires.

RS422

RS-422 standard has now been superseded by the RS-485 standard which adds additional features to the RS-422 standard.

RS422’s advantages1. Long Distance Runs - Up to 500 feet is generally

supported, and with repeaters, even further distances can be achieved.

2. Multi-Drop - Usually, up to 32 devices can be connected per port, and even more using repeaters. Devices are distinguished by unique addresses that are assigned to each device. For example, if you have 5 devices attached to a port, they would be addressed as units 1 to 5. The addresses can be set via switches or software, depending on the design of the device.

3. Noise Resistant - Since it uses a separate FLOATING transmit and receive pair (four wires), it offers better noise immunity than RS-232.

RS485

EIA-485, also known as TIA/EIA-485 or RS-485, is a standard defining the electrical characteristics of drivers and receivers for use in balanced digital multipoint systems. RS485 standard can be used effectively over long distances and in electrically noisy environments.

RS485 converter

USB_RS485 Converter

RS485RS-485 allows for serial connections

among more than two devices on a networked system. A RS-485 compliant network is a multi-point communications network. Multiple receivers may be connected to such a network in a linear, multi-drop configuration.

The equipment located along a set of EIA-485 wires are interchangeably called nodes, stations and devices.

usb-rs485-cable

RS485

RS-485 drivers are now even able to

withstand bus contention problems

and bus fault conditions.EIA-485 signals are used in a wide

range of computer and automation

systems. It is used for low-speed data

communications in commercial aircraft

cabins vehicle bus. It requires minimal

wiring, and can share the wiring

among several seats, reducing weight.

Rs485 pinout

RS485

EIA-485 is also used in building automation as the simple bus wiring and long cable length is ideal for joining remote devices. It may be used to control video surveillance systems or to interconnect security control panels and devices such as access control card readers.

USB-to-RS485-Cable-ZT-RS485

rs485-usb

main differences between 2-wire RS-485 and RS-422

1. RS-485 can have multiple Commanding Devices

and multiple Listening Devices. RS-422 can have

only one Commander and multiple Listeners.

2. RS-485 wiring is easier since you are only

dealing with 2 wires instead of 4.

3. Programming RS-485 is more difficult, since you

are sending and receiving on the same two wires,

you need to enable and disable the transmitter at

the correct time so that you may perform proper

communications.

Differences between RS232, RS422 and RS485

SPECIFICATIONS RS232 RS423 RS422 RS485

Mode of OperationSINGLE-ENDED

SINGLE-ENDED

DIFFERENTIAL DIFFERENTIAL

Total Number of Drivers and Receivers on One Line (One driver active at a time for RS485 networks)

1 DRIVER1 RECVR

1 DRIVER10 RECVR

1 DRIVER10 RECVR

32 DRIVER32 RECVR

Maximum Cable Length 50 FT. 4000 FT. 4000 FT. 4000 FT.

Maximum Data Rate (40ft. - 4000ft. for RS422/RS485) 20kb/s 100kb/s 10Mb/s-100Kb/s 10Mb/s-100Kb/s

Maximum Driver Output Voltage +/-25V +/-6V -0.25V to +6V -7V to +12V

Driver Output Signal Level (Loaded Min.)

Loaded +/-5V to +/-15V +/-3.6V +/-2.0V +/-1.5V

Driver Output Signal Level (Unloaded

Max)Unloaded +/-25V +/-6V +/-6V +/-6V

Driver Load Impedance (Ohms) 3k to 7k >=450 100 54

Max. Driver Current in High Z State

Power On N/A N/A N/A +/-100uA

Max. Driver Current in High Z State

Power Off +/-6mA @ +/-2v +/-100uA +/-100uA +/-100uA

usb_converter_RS485_RS422_RS232_converter_usb

RS232 and RS485

CADA, ARVIN PATRICKGAMBOA, FRENCESS LHOUPERMIGONES, SHYLEE MAY

BSCpE IV 01-17-12

SAMONTE, CHARISSE ANNEUY, LORADEL