serial_communication_tutorial_combined.pdf

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Multiport Serial Board Solutions

RS-232SerialCommunicationTutorial

The most common and easy-to-use serial communication interface

RS-232 Serial Communication Tutorial

RS-232 is a straightforward, universal, and commonly implemented

serial interface. Despite its limited 15 m transmission distance, its

low cost and easy wiring features make RS-232 the first choice

for many applications. RS-232 establishes two-way (full-duplex)

communications, with signals represented by voltage levels

measured with respect to a system common ground (power/logic

ground). The idle state (MARK) is negative with respect to the

common ground, and the active state (SPACE) is positive with

respect to common ground.

RS-232 Data Format

Start bit: Always 1

Data bits: 5, 6, 7, or 8 bits

Parity: None, Odd, Even, Space, Mark

Stop bit: 1, 1.5 (Data bits = 5), or 2 bits

RS-232 Specs

Standard Feature Mode ofOperation

Drivers perLine

Receivers perLine

Max. CableLength

Max. Data Rate

EIA RS-232 Point to point Single Ended 1 1 50 feet 20 Kbps

RS-232 Signal Definition

The standard output signal level of RS-232 usually varies

between +12V and -12V, with a dead area between +3V

and -3V designed to absorb line noise. The TTL signal from the

UART is between 0 and 5 volts, but after being transformed by

the RS-232 transceiver, the signal voltage is changed to +12V

to -12V.

TxD Transmit Data

RxD Receive Data

RTS Request to Send

CTS Clear to Send

DTR Data Terminal ReadyDSR Data Set Ready

DCD Data Carrier Detect

GND Ground

Sirius House, Peel Street, Southampton SO14 5QT, UK Tel: 44 (0)23 80571177 [email protected] www.captec.ws

Karlsruher Strasse 11/1, D-70771, Leinf.-Echterdingen, Germany Tel: 49 (0)711 22063000 [email protected] www.captec-gmbh.deCaptec GmbH

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Total Solution for Industrial Device NetworkingRS-23

2SerialCommunicationTutorial

Flow Control

H/W Flow ControlRTS and CTS signals are often used for H/W flow control.

When a station is ready to receive, it raises the RTS signal to

request transmit signals from the remote side.

S/W Flow Control

Sending an XON/XOFF pattern is a typical way to control data

flow. When a station is ready to receive, the S/W sends an

XON pattern. If the Rx buffer is almost full, the S/W sends an

XOFF pattern to ask the remote side not to transmit.

An Easy Programming ToolMOXA PComm Library

Main Features

Software developers are often confused by Microsofts

complex Win32 COMM API, used to develop serial comm

applications under Windows XP, Windows 2000, Windows

NT, and Windows 95/98/ME. The confusion stems from the

fact that Win32 COMM API is a general purpose utility, with

very complex syntax. MOXA PComm Pro offers you a better

solution.

50 easy-to-use API Functions

Supports VB, C/C++, Delphi Interface

Compatible with Win32 Comm API Superior Troubleshooting Utilities

Supports Z/Y/XModem, Kermit, and ASCII protocols

Performance Analyzer

Data Scope



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RS-422/485SerialCommuicationTutorial

Whats Needed for Industrial Applications

Standard EIA RS-422A

Feature Full-duplex,

Point to point

Mode of

Operation

Differential

Drivers per Line 1

Receivers per Line 10

Maximum CableLength

4000 feet

Maximum Data

Rate

10 Mbps

RS-422/485 SerialCommunication Tutorial

Most devices used in todays industrial environments are

designed for use with the RS-422/485 interface. This means

that many users employ RS-422/485 serial communication

boards in their PCs, allowing the PCs to connect to an industrial

RS-422 or RS-485 network and transmit data over distancesup to 1.2 km. The RS-422/485 standards overcome the

transmission distance limitation by using a differential signal for

transmitting data and control signals. In addition to distance

and multi-drop issues for industrial applications, isolation,

housing, wiring, power supply, and over-surge protection are

also important issues.

RS-422

RS-485

Differential Transmission

The RS-422 protocol greatly expands the

practical possibilities of the serial bus. It

provides a mechanism by which data can

be transmitted over long distances (up

to 4,000 feet) and at very high speeds

(up to 10 Mbps). This is accomplished by

using differential technology that splitseach signal into two separate wires in

opposite voltage states, making this

type of wiring configuration well suited

for noisy environments.

Multidrop Network

RS-485 is an updated version of RS-422

that is specifically designed to address

the problem of communication between

multiple devices on a single data line. It

is a balanced transmission system with

the ability to allow up to 32 devices to

communicate using the same data line.

This is achieved with tri-statable drivers that

are usually controlled by a programmable

handshake line to ensure that only one

device acts as a driver at any given time.

Standard EIA RS-485

Feature Half-duplex,

multi-dropMode of

Operation

Differential

Drivers per Line 32

Receivers per Line 32

Maximum Cable

Length

4000 feet

Maximum Data

Rate

10 Mbps



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Total Solution for Industrial Device Networking

Limitations:

*System must determine when to switch the transmitter on and off.

*Only one node can switch on/off at any given time.

Traditional Solution:

Use the RTS signal to control the transmitter by software.

Advanced Method:

ADDC(Automatic Data Direction Control).

Benefit:

ADDCswitches the transmitter on and off very precisely

by hardware, effectively simplifying the complexity of timing control by software.

Result:

The Industrial Multiport Communication Board uses embedded ADDC technology to automatically sense and control data

direction instead of using RTS/CTS control, making the handshaking signal method obsolete.

Termination

Industrial Wiring Peripheral

* Terminal Block* DIN-Rail Mounting

RS-42

2/485SerialCommu

icationTutorial

Termination is used to match impedance of both receive and

transmission nodes. When impedance is mismatched, the

transmitted signal is not completely absorbed by the load

and a portion is reflected back into the transmission line. If

the transmission line and load impedance are equal, these

signal reflections are eliminated. The value of resistor needed

to match the characteristic impedance is specified by the cable

manufacturer, with a commonly used value of 120 ohms.

ADDC(Automatic Data Direction Control)

Isolation: Eliminate Ground Loops!

A common problem in many industrial applications is ground loop

currents that flow through the ground line when ground voltage levels

differ between connected devices. To eliminate this problem, Moxas

Industrial boards and full function converters are available with Optical

Isolation up to 2000V.

Five questions you need to ask about RS-422/485 selection:

1. What is the system configuration?

(2/4-wire RS-422/485)

2. Are Isolation or Surge Protection available?

3. What value of termination resistors are used?

4. Is the resistor setup easily modified?

5. What baud rate, or range of baud rates, are supported?

TB-F9 TB-M9



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RS-422/485SerialCommuicationTutorial

Moxa RS-422/485 Solutions

Industrial Board Comparison Chart

Supported OS DriversMOXAs industrial COM port driver not

only supports all major operating systems,

but also the following dedicated operating

systems for customers special needs.

DOS (all Industrial Boards)

OS/2 (ISA)

SCO XENIX (ISA)

QNX4 (ISA)

QNX 6.x (PCI)

Linux

Industrial Board Selection Guide

Model CI-132 CI-132I CI-132IS CP-132 CP-132I CP-132S CP-132IS CA-132 CA-132I CI-134 CI-134I CP-114 CP-114I CP-114S CP-114IS

Bus ISA PCI PC/104 ISA PCI

No. of Ports 2 4

I/O Control-

ler16C550C

Connector

TypeDB9 Male x 2 PC/104

DB37 Female (with Optional accessories to 4 DB9/DB25 Male Con-

nectors)

Interface RS-422/485 RS-232/422/485

Speed 50-921.6 Kbps

RS-485

IntelligenceADDC

Parity None, Even, Odd, Space, Mark

Surge

Protection

Isolation

Data Bits 5, 6, 7, 8

Stop Bits 1, 1.5, 2

IRQ2(9), 3, 4, 5, 7, 10 (Default),

11, 12, 15Assigned by BIOS

3, 4, 5, 6, 7, 9, 10,

11, 12, or 15

2(9), 3, 4, 5, 7,

10 (Default), 11,

12, 15

Assigned by BIOS

I/O Address 0X0000-0xFFFF,

Default: 0x 180

Assigned by BIOS0X0000-0xFFFF,

Default: 0x 180

Assigned by BIOS

Operating

Temp0-55C



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Total Solution for Industrial Device Networking

RS-422/485 Wiring Topology

RS-422

/485SerialCommuic

ationTutorial

4-Wire Full Duplex (Point-to-Point)

2-Wire Half Duplex (Point-to-Point)

2-Wire Half Duplex (Multi-Drop)

4-Wire Full Duplex (Multi-Drop)

RS-422

RS-485

RS-485

RS-485



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serial_communication_tutorial_combined.pdf

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