HISTORY AND THEORY OF SERIAL COMMUNICATIONS

Circa 1960

HISTORY

RS-232 was first introduced in 1962 by the Radio Sector of

the Electronic Industries Alliance (Bell Systems driven)

 teleprinter (teletypewriter, Teletype or TTY) is an 

electromechanical typewriter that can be used to

communicate typed messages from point to point and 

point to multipoint over a variety of communication channels

that range from a simple electrical connection, such as a pair

of wires, to the use of radio and microwave as the 

transmission medium

HISTORY

Allowed Journalist to get articles to the newspaper

faster.

Previously had to send stories snail mail

Now they could go to the local MA BELL office and

wait in line to transcribe their story into a dumb

terminal.

HISTORY

HISTORY

RS232 was adopted my the first computer manufactures

Predecessors to USB devices.

Two Types

Data Terminal Equipment

AKA….DTESLC/PLC5/Logix

Family (Channel 0)COMPUTER COM

ports

Data Communication Equipment

AKA….DCEModems, PrintersDF1 PanelViews =

2711-xxx16, -xxx17DH485 (RS232)

PanelViews = 2711-xxx5, -xxx9

Cable Requirements

To connect a DTE device to DTE device a null modem cable is needed.

To connect a DTE device to DCE device a straight thru cable is needed.

To connect a DCE device to DCE device a null modem cable is needed

Cable Requirements

To connect a AB PLC to PC you need a Null Modem Cable

To connect a PC to a Panel View you need a straight thru or null modem adapter

A null modem cable with a null modem adapter connected becomes a straight thru cable.

AB typical null modem cablefull duplex

Signal OriginDB-

9 pinName Typical purposeAbbreviation

DTE DCE

Data Terminal Ready

Indicates presence of DTE to DCE. DTR ● 4

Data Carrier Detect

DCE is connected to the telephone line. CD ● 1

Data Set Ready

DCE is ready to receive commands or data. DSR ● 6

Ring Indicator

DCE has detected an incoming ring signal on the telephone line. (Unused)

RI ● 9

Request To Send

DTE requests the DCE prepare to receive data. RTS ● 7

Clear To Send

Indicates DCE is ready to accept data. CTS ● 8

Transmitted Data

Carries data from DTE to DCE. TxD ● 3

Received Data

Carries data from DCE to DTE. RxD ● 2

Common Ground

GND common 5

AB typical null modem cablefull duplex

Right Click and select Acrobat Document then open

AB cable Pinout

Click file to open

1747-CP3_1756-CP3-PinOut.pdf

1761-CBL-AS03 & 1761-CBL-AS09 Cable Pin-Out.pdf 1761-CBL-PM02-PinOut.pdf

1784-CAK-PinOut.pdf

1784-CP3-PinOut.pdf

1784-CP10-PinOut.pdf

2711-NC21 and 2711-NC22 cables for the PanelView.pdf

Null modem cable using only 3 wires full duplex.

Signal OriginDB-

9 pinName Typical purposeAbbreviation

DTE DCE

Data Terminal Ready

Indicates presence of DTE to DCE. DTR ● x

Data Carrier Detect

DCE is connected to the telephone line. CD ● x

Data Set Ready

DCE is ready to receive commands or data. DSR ● x

Ring Indicator

DCE has detected an incoming ring signal on the telephone line. (Unused)

RI ● x

Request To Send

DTE requests the DCE prepare to receive data. RTS ● x

Clear To Send

Indicates DCE is ready to accept data. CTS ● x

Transmitted Data

Carries data from DTE to DCE. TxD ● 3

Received Data

Carries data from DCE to DTE. RxD ● 2

Common Ground

GND common 5

Full Duplex VS Half Duplex

Full DuplexSend and Receive

data at the same time

Phone

Half DuplexLimited to only

Send or Receive at the same time

Walkie-Talkie

Common AB Baud Rates in Bits Per Second

300, 600, 1200, 2400,48009600 (Default for most SLC series)19200 (Standard Max Rate setting for

SLC series)38.4 K Max rate in control logix and

newer micro logix

Typical RSLinx serial Config Screen

What does UPLOAD and DOWNLOAD mean?

This can change with the make of the PLCWe will talk about the most common

version and the one AB uses.Download means taking information from

the programming terminal to the PLC or Device.

Upload means taking information from PLC or Device into the programming terminal.

Support

Rockwell Knowledge Base https://rockwellautomation.custhelp.com/app/home

GoogleRockwell Tech 1-440-646-3100Email MeFree Starter Software http://

www.ab.com/linked/programmablecontrol/plc/micrologix/downloads.html

http://www.rockwellautomation.com/rockwellsoftware/design/rslogix5000/demo.html