Siemens Simatic S7-400 Technical Document

SIMATIC
S7-400
Point-to-point connection CP 440
Installation and Parameter
Assignment
Equipment Manual
03/2022
A5E00057742-AE
Preface
Product Description 1
Basic Principles of Serial
Data Transmission 2
Commissioning the CP 440 3
Mounting the CP 440 4
Con󹪝guring and Parameter
Assignment the CP 440 5
Communication via
Function Blocks 6
Startup Characteristics and
Operating Mode Transitions
of the CP 440 7
Diagnostics with the CP 440 8
Programming Example for
Standard Function Blocks 9
Technical speci󹪝cations 10
Connecting cables 11
Accessories and order
numbers 12
Literature 13

Legal information
Warning notice system
This manual contains notices you have to observe in order to ensure your personal safety, as well as to prevent damage
to property. The notices referring to your personal safety are highlighted in the manual by a safety alert symbol, notices
referring only to property damage have no safety alert symbol. These notices shown below are graded according to
the degree of danger.
DANGER
indicates that death or severe personal injury will result if proper precautions are not taken.
WARNING
indicates that death or severe personal injury may result if proper precautions are not taken.
CAUTION
indicates that minor personal injury can result if proper precautions are not taken.
NOTICE
indicates that property damage can result if proper precautions are not taken.
If more than one degree of danger is present, the warning notice representing the highest degree of danger will be
used. A notice warning of injury to persons with a safety alert symbol may also include a warning relating to property
damage.
Quali󹪝ed Personnel
The product/system described in this documentation may be operated only by personnel quali󹪝ed for the speci󹪝c
task in accordance with the relevant documentation, in particular its warning notices and safety instructions.
Quali󹪝ed personnel are those who, based on their training and experience, are capable of identifying risks and
avoiding potential hazards when working with these products/systems.
Proper use of Siemens products
Note the following:
WARNING
Siemens products may only be used for the applications described in the catalog and in the relevant technical
documentation. If products and components from other manufacturers are used, these must be recommended or
approved by Siemens. Proper transport, storage, installation, assembly, commissioning, operation and maintenance
are required to ensure that the products operate safely and without any problems. The permissible ambient
conditions must be complied with. The information in the relevant documentation must be observed.
Trademarks
All names identi󹪝ed by ® are registered trademarks of Siemens AG. The remaining trademarks in this publication may
be trademarks whose use by third parties for their own purposes could violate the rights of the owner.
Disclaimer of Liability
We have reviewed the contents of this publication to ensure consistency with the hardware and software described.
Since variance cannot be precluded entirely, we cannot guarantee full consistency. However, the information in this
publication is reviewed regularly and any necessary corrections are included in subsequent editions.
Siemens AG
Digital Industries
Postfach 48 48
90026 NÜRNBERG
GERMANY
A5E00057742-AE
Ⓟ 04/2022 Subject to change
Copyright © Siemens AG 2022.
All rights reserved

Preface
Preface
Purpose of This Manual
This manual explains how to con󹪝gure and operate a point-to-point connection.
Contents of the manual
The manual describes the hardware and software of the CP 440 communication processor and
its integration in an S7–400 programmable controller. It is divided up into instruction-based
chapters and a reference section (appendices).
The following subjects are covered:
• The basics of point-to-point communication with the CP 440
• Commissioning the CP 440
• Mounting the CP 440
• Communication via the CP 440
• Troubleshooting
• Application examples
• Properties and technical speci󹪝cations
Scope of the manual
This manual is valid for the "CP 440 with X27 RS 422/485 interface", order number: "6ES7 440–
1CS00–0YE0" as of version "01".
Note
The description of the CP 440 communication processor in this manual were correct at the time
of publication. We reserve the right to describe modi󹪝cations to the functionality of the modules
in a separate Product Information.
Recycling and Disposal
The CP 440 is an environment-friendly product. It's characteristic features include:
• Halogen-free plastics used for housing, which nonetheless has a high degree of 󹪝re resistance
• Laser inscriptions (i.e. no labels)
Point-to-point connection CP 440 Installation and Parameter Assignment
Equipment Manual, 03/2022, A5E00057742-AE 3

• Plastics identi󹪝cation in accordance with DIN EN ISO 11469
• Less material used because the unit is smaller and with fewer components thanks to
integration in ASICs
The CP 440 is suitable for recycling on account of the low level of contaminants in its
components. Please contact a certi󹪝ed waste disposal company for eco-friendly recycling and to
dispose of your old devices.
Structure of This Manual
To help you to quickly 󹪝nd the information you require, this manual o󹪜ers the following:
• At the beginning of the manual you can 󹪝nd a comprehensive list of contents.
• Finally, a comprehensive index allows quick access to information on speci󹪝c subjects.
Additional assistance
Please contact your local Siemens representative if you have any queries about the products
described in this manual.
• Find your contact partner at:
http://www.siemens.de/automation/partner (http://www.siemens.com/automation/
partner)
• You will 󹪝nd the guide to the technical documentation for the individual SIMATIC products
and systems at:
http://www.siemens.de/simatic-doku (http://www.siemens.com/simatic-doku)
• The online catalog and the online ordering system are available at:
http://www.siemens.de/automation/mall (http://www.siemens.com/automation/mall)
Training Center
We o󹪜er a range of courses to help get you started with the S7 automation system. Please
contact your local training center or the central training center in Nuremberg,
D-90327 Germany.
• Internet: http://www.siemens.com/sitrain (http://www.siemens.com/sitrain)
Technical support
Here you can access Technical Support for all A&D products
• Use the Web form for the support request
http://www.siemens.com/automation/support-request (http://www.siemens.com/
automation/support-request)
Additional information about our technical support is available in the Internet at:
http://www.siemens.de/automation/service&support (http://www.siemens.com/automation/
service&support)
Preface
Point-to-point connection CP 440 Installation and Parameter Assignment
4Equipment Manual, 03/2022, A5E00057742-AE

Service & Support on the Internet
In addition to our documentation, we o󹪜er a comprehensive knowledge base online on the
Internet.
http://www.siemens.de/automation/service&support (http://www.siemens.com/automation/
service&support)
There you will 󹪝nd:
• The newsletter, which provides the latest information on your products.
• The documents you require, using our Service & Support search engine.
• A forum where users and specialists exchange information worldwide.
• Your local service partner for Automation & Drives in our contact database.
• Information about on-site service, repairs and spare parts. And much more is available under
"Services".
Preface
Point-to-point connection CP 440 Installation and Parameter Assignment
Equipment Manual, 03/2022, A5E00057742-AE 5

Preface
Point-to-point connection CP 440 Installation and Parameter Assignment
6Equipment Manual, 03/2022, A5E00057742-AE

Table of contents
Preface ................................................................................................................................................... 3
1 Product Description ............................................................................................................................. 11
1.1 Uses of the CP 440............................................................................................................. 11
1.2 Components Required for a Point-to-Point Connection with the CP 440............................... 12
1.2.1 Required Hardware Components ........................................................................................ 12
1.2.2 Required Software Components ......................................................................................... 13
1.2.3 Incompatible CPU versions ................................................................................................. 13
1.3 Design of the CP 440.......................................................................................................... 14
1.4 Features of the X27 (RS 422/485) Interface ........................................................................ 16
2 Basic Principles of Serial Data Transmission ........................................................................................ 17
2.1 Serial Transmission of a Character ...................................................................................... 17
2.2 Transmission Procedure with a Point-to-Point Connection ................................................... 20
2.3 Transmission integrity ........................................................................................................ 21
2.4 Data Transmission with the ASCII Driver.............................................................................. 23
2.4.1 Data Transmission with the ASCII Driver.............................................................................. 23
2.4.2 Sending Data with the ASCII Driver..................................................................................... 24
2.4.3 Receiving Data with the ASCII Driver................................................................................... 26
2.4.4 Topologies Between the Communication Partners .............................................................. 32
2.5 Data Transmission with the 3964(R) Procedure................................................................... 35
2.5.1 The Control Characters of the 3964(R) Procedure ............................................................... 35
2.5.2 Block Checksum................................................................................................................. 37
2.5.3 Sending Data with 3964(R) ................................................................................................ 38
2.5.4 Receiving Data with 3964(R) .............................................................................................. 41
2.5.5 Handling Corrupt Data ....................................................................................................... 46
3 Commissioning the CP 440 .................................................................................................................. 49
4 Mounting the CP 440 ........................................................................................................................... 53
4.1 CP 440 slots....................................................................................................................... 53
4.2 Mounting and Dismounting the CP 440.............................................................................. 53
4.2.1 Installation steps................................................................................................................ 54
4.2.2 Removal steps.................................................................................................................... 54
5Con󹪝guring and Parameter Assignment the CP 440 ........................................................................... 55
5.1 Assigning parameters to the CP 440 ................................................................................... 55
5.2 Installing the Programming Interface ................................................................................. 56
5.3 Parameters for the Communications Protocols.................................................................... 56
5.4 Con󹪝guration data ............................................................................................................. 57
5.4.1 Introduction....................................................................................................................... 57
Point-to-point connection CP 440 Installation and Parameter Assignment
Equipment Manual, 03/2022, A5E00057742-AE 7

5.4.2 Basic Parameters of the CP 440 .......................................................................................... 57
5.4.3 Con󹪝guration Data of the ASCII Driver ................................................................................ 58
5.4.4 Con󹪝guration Data of the 3964(R) Procedure ..................................................................... 63
5.5 Managing the Parameter Data............................................................................................ 68
5.6 Firmware updates .............................................................................................................. 69
5.6.1 Subsequent Loading of Firmware Updates.......................................................................... 69
5.6.2 Viewing the Firmware Version............................................................................................ 71
6 Communication via Function Blocks.................................................................................................... 73
6.1 Overview of the Function Blocks ........................................................................................ 73
6.2 Notes on Program Structure ............................................................................................... 75
6.3 Using the Function Blocks .................................................................................................. 75
6.3.1 S7 Transmits Data to a Communication Partner, 10 SEND_440 FB ....................................... 76
6.3.2 S7 Receives Data from a Communication Partner, 9 RECV_440 FB ....................................... 79
6.3.3 Deleting the Receive Bu󹪜er (11 "RES_RECV" FB) .................................................................. 82
6.4 Programming the Function Blocks ...................................................................................... 85
6.4.1 Supplying the block parameters ......................................................................................... 85
6.5 General Information on Program Processing ....................................................................... 88
6.6 Technical Speci󹪝cations of the Function Blocks ................................................................... 89
7 Startup Characteristics and Operating Mode Transitions of the CP 440 ............................................. 91
7.1 Operating Modes of the CP 440.......................................................................................... 91
7.2 Startup Characteristics of the CP 440.................................................................................. 91
7.3 Behavior of the CP 440 on Operating Mode Transitions of the CPU...................................... 92
7.4 Behavior of the Sender Line Drivers of the Serial Interface During Particular Operating
Modes of the CP 440.......................................................................................................... 93
8 Diagnostics with the CP 440 ................................................................................................................ 95
8.1 Diagnostics Functions of the CP 440................................................................................... 95
8.2 Diagnostics via the display elements of the CP 440 ............................................................. 96
8.3 Diagnostics Messages of the Function Blocks...................................................................... 97
8.4 Diagnostics via the diagnostic bu󹪜er of the CP 440........................................................... 104
9 Programming Example for Standard Function Blocks ....................................................................... 107
9.1 General Information......................................................................................................... 107
9.2 Device Con󹪝guration........................................................................................................ 107
9.3 Settings ........................................................................................................................... 108
9.4 Blocks Used ..................................................................................................................... 108
9.5 Installation, Error Messages.............................................................................................. 111
9.6 Activation, Startup Program and Cyclic Program ............................................................... 111
9.6.1 "CP440 SEND RECV" Program Example.............................................................................. 111
9.6.2 "CP440 1 CYC" Program Example ...................................................................................... 113
9.6.3 "CP440 ASCII BCC" Program Example ................................................................................ 113
Table of contents
Point-to-point connection CP 440 Installation and Parameter Assignment
8Equipment Manual, 03/2022, A5E00057742-AE

9.6.4 "CP440 MASTER" Program Example .................................................................................. 114
9.6.5 "CP440 SLAVE" Program Example ..................................................................................... 115
10 Technical speci󹪝cations ..................................................................................................................... 117
10.1 Technical Speci󹪝cations of the CP 440 .............................................................................. 117
10.2 Standards and approvals .................................................................................................. 120
10.2.1 Currently valid markings and approvals ............................................................................ 120
10.2.2 CE approval ..................................................................................................................... 121
10.2.3 CCC approval ................................................................................................................... 122
10.2.4 UKCA approval................................................................................................................. 122
10.2.5 Explosion protection ........................................................................................................ 123
10.2.6 cULus approval ................................................................................................................ 124
10.2.7 cULus HAZ. LOC. approval ................................................................................................ 124
10.2.8 cFMus approval................................................................................................................ 124
10.2.9 Approval for Australia and New Zealand ........................................................................... 125
10.2.10 Approval for the Korea and South Korea ........................................................................... 125
11 Connecting cables ............................................................................................................................. 127
11.1 X27 (RS 422/485) Interface of the CP 440......................................................................... 127
11.2 Cables ............................................................................................................................. 127
12 Accessories and order numbers......................................................................................................... 133
12.1 Accessories and Order Numbers ....................................................................................... 133
13 Literature ........................................................................................................................................... 135
13.1 Literature on SIMATIC S7.................................................................................................. 135
Index .................................................................................................................................................. 137
Table of contents
Point-to-point connection CP 440 Installation and Parameter Assignment
Equipment Manual, 03/2022, A5E00057742-AE 9

Table of contents
Point-to-point connection CP 440 Installation and Parameter Assignment
10 Equipment Manual, 03/2022, A5E00057742-AE

Product Description 1
1.1 Uses of the CP 440
Applications
The CP 440 communication processor enables you to exchange data between automation
devices or computers by means of a point-to-point connection. The CP 440 is designed to
transfer short, fast frames.
The following are typically connected to it:
• Scanners, barcode readers
• Sensors
• Weighing scales
Functionality of the CP 440
The CP 440 communication processor provides the following functionality:
• An integrated MPI (Multipoint) X27 (RS422/485) interface
• Maximum transmission length 400 bytes (also see chapter "Overview of the Function Blocks
(Page 73)")
• A transmission rate of up to 115.2 kbps, full-duplex
• Integration of the most important transmission protocols in the module 󹪝rmware
– ASCII driver
– 3964(R) Procedure
• Customization of the transmission protocols by means of parameter assignment with the CP
440: Point-to-Point Communication, Parameter Assignment interface
Uses of the CP 440
The CP 440 communication processor allows point-to-point communication with SIMATIC
modules and with non-Siemens products.
Point-to-point connection CP 440 Installation and Parameter Assignment
Equipment Manual, 03/2022, A5E00057742-AE 11

Functions Supported by the Interfaces
Table 1-1 Functions of the CP 440
Function CP 440
RS 422* RS 485*
3964(R) Procedure Yes No
ASCII driver: Yes Yes
• XON/XOFF 󹪞ow control Yes No
* The RS 422 and RS 485 are distinguished by their parameter con󹪝guration.
1.2 Components Required for a Point-to-Point Connection with the CP
440
1.2.1 Required Hardware Components
Hardware Components
The following table lists the hardware components required for establishing a point-to-point
connection with the CP 440.
Table 1-2 Hardware Components for a Point-to-Point Connection with the CP 440
Components Function Diagram
Rack ... provides the mechanical and electrical
connections of the S7-400.
Power supply module (PS) ... converts the line voltage (120/230 V AC
or 24 V DC) into the operating voltage of 24
V and 5 V DC required to supply the S7-400.
Central processor unit (CPU)
Some CPU versions cannot be used with
the CP 440.
Accessories: Memory card, backup battery
... executes the user program; communi‐
cates via the MPI interface with other CPUs
or with a programming device.
CP 440 communication processor ... communicates via the interface with one
or more communication partners.
Standard cable ... connects the CP 440 communication
processor to the communication partner.
Programming device cable ... connects a CPU to a programming device/
PC.
Programming device or PC ... communicates with the CPU of the
S7-400.
Product Description
1.2 Components Required for a Point-to-Point Connection with the CP 440
Point-to-point connection CP 440 Installation and Parameter Assignment
12 Equipment Manual, 03/2022, A5E00057742-AE

1.2.2 Required Software Components
Software components
The following table lists the software components required for establishing a point-to-point
connection with the CP 440.
Table 1-3 Software Components for a Point-to-Point Connection with the CP 440
Components Function Diagram
STEP 7 software package ... con󹪝gures, assigns parameters, pro‐
grams and tests the S7-400.
+License
Parameter assignment interface: Point-to-
Point Communication, Parameter As‐
signment interface, Version 5.1
... assigns parameters for the interfaces of
the CP 440.
Function blocks (FBs) with programming
examples
... controls the communication between
CPU and CP 440.
1.2.3 Incompatible CPU versions
CPU versions
The CP 440 can be operated with all CPU versions except the CPUs listed in the tables below:
Table 1-4 CPU Versions with Which the CP 440 Can Be Used as of the Version Indicated
CPU Order number
CPU 412-1 6ES7 412-1XF01-0AB0, Release 5
CPU 413-1 6ES7 413-1XG01-0AB0, Release 5
CPU 413-2 6ES7 413-2XG01-0AB0, Release 5
CPU 414-1 6ES7 414-1XG01-0AB0, Release 5
CPU 414-2 with 128k 6ES7 414-2XG01-0AB0, Release 5
CPU 414-2 with 348k 6ES7 414-2XJ00-0AB0, Release 7
CPU 416-1 6ES7 416-1XJ01-0AB0, Release 5
CPU 416-2 with 0.8 M 6ES7 416-2XK00-0AB0, Release 7
CPU 416-2 with 1.6 M 6ES7 416-2XL00-0AB0, Release 7
CPU 416-2 DP ISA Lite
CPU 416-2 DP ISA
CPU 412-2 DP PCI
CPU 416-2 DP PCI
6ES7 616-2PK00-0AB4, Release 3
Product Description
1.2 Components Required for a Point-to-Point Connection with the CP 440
Point-to-point connection CP 440 Installation and Parameter Assignment
Equipment Manual, 03/2022, A5E00057742-AE 13

Table 1-5 CPU Versions with Which the CP 440 Cannot be Used
CPU Order number
CPU 412-1 6ES7 412-1XF00-0AB0
CPU 413-1 6ES7 413-1XG00-0AB0
CPU 413-2 6ES7 413-2XG00-0AB0
CPU 414-1 6ES7 414-1XG00-0AB0
CPU 414-2 with 128k 6ES7 414-2XG00-0AB0
CPU 416-1 6ES7 416-1XJ00-0AB0
1.3 Design of the CP 440
Interface
The CP 440 communication processor is supplied with an integrated serial X27 (RS422/485)
interface.
Product Description
1.3 Design of the CP 440
Point-to-point connection CP 440 Installation and Parameter Assignment
14 Equipment Manual, 03/2022, A5E00057742-AE

Position of Operator Control and Display Elements
The 󹪝gure shows the arrangement of the controls and indicators on the front panel of the CP 440
communication processor.
&3,17)(;7))$8/77['5['9)LUPZDUHYHUVLRQ,QWHJJUDWHG;56LQWHUIDFH
Figure 1-1 Arrangement of the Controls and Indicators on the CP 440 Communication Processor
LEDs
On the front panel of the
• INTF (red) indicates an internal error
• EXTF (red) indicates an external error
• FAULT (red) Fault display for interface
• TXD (green) Interface sending
• RXD (green) Interface receiving
Base Connector for S7 Backplane Bus
On the back panel of the CP 440 you will 󹪝nd the base connector for the S7-400 backplane bus.
Product Description
1.3 Design of the CP 440
Point-to-point connection CP 440 Installation and Parameter Assignment
Equipment Manual, 03/2022, A5E00057742-AE 15

The S7-400 backplane bus is a serial data bus via which the CP 440 communicates with the
modules of the programmable controller.
1.4 Features of the X27 (RS 422/485) Interface
De󹪝nition
The X27 (RS 422/485) interface is a voltage-di󹪜erence interface for serial data transmission in
compliance with the X27 standard.
Properties
The X27 (RS 422/485) interface has the following attributes and is in compliance with the
following requirements:
• Type: Di󹪜erential voltage interface
• Front connector: 15-pin sub-D female with screwed interlock
• Max. transmission rate: 115.2 Kbps
• Max. cable length: 1200 m at 19200 Bps
• Standard: DIN 66259 Parts 1 and 3, EIA-RS 422/485, CCITT V.11
• Degree of protection: IP 00
Note
With the RK 512 and 3964(R) protocols, the X27 (RS 422/485) interface submodule can only be
used in four-wire mode.
Cables
Siemens o󹪜ers standard cables in various lengths for point-to-point connection between the
communication processor and a communication partner.
For order information and the length of standard cables are listed in the appendix
"AUTOHOTSPOT".
Fabricating Your Own Cables
If you are fabricating your own cables, there are a few points to take into consideration. The
appendix "AUTOHOTSPOT" of this manual contains information about this topic as well as the pin
assignment of the sub D male connector and the wiring diagrams.
Product Description
1.4 Features of the X27 (RS 422/485) Interface
Point-to-point connection CP 440 Installation and Parameter Assignment
16 Equipment Manual, 03/2022, A5E00057742-AE

Basic Principles of Serial Data Transmission 2
2.1 Serial Transmission of a Character
Introduction
The system provides various networking options for the exchange of data between two or more
communication partners. The simplest form of data interchange is via a point-to-point
connection between two communication partners.
Point-to-Point Communication
In point-to-point communication the communication processor forms the interface between a
programmable controller and a communication partner. Data are transmitted serially in the
point-to-point connection with the CP 440.
Serial Transmission
In serial transmission, the individual bits of each byte of information are transmitted one after
the other in a 󹪝xed order.
Drivers for Bidirectional Data Tra󹪟c
The CP 440 itself handles data transmission with communication partners via its serial interface.
The CP 440 is equipped with two di󹪜erent drivers for this purpose.
Bidirectional data tra󹪟c:
• ASCII driver
• 3964(R) procedure
The CP 440 executes data transfer via the serial interface depending on the selected driver.
Bidirectional Data Tra󹪟c - Operating Modes
The CP 440 has two operating modes for bidirectional data tra󹪟c:
• Half-duplex operation (3964(R) procedure, ASCII driver)
Data is exchanged between the communication partners but only in one direction at a time.
In half-duplex operation, therefore, at any one time data is being either sent or received. The
exception to this may be individual control characters for data 󹪞ow control (e.g. XON/XOFF),
which can also be sent during a receive operation or received during a send operation.
• Full-duplex operation (ASCII driver)
Data is exchanged between two or more communication partners in both directions
simultaneously. In full-duplex operation, therefore, data can be sent and received at the
same time. Every communication partner must be able to operate a send and a receive
facility simultaneously.
Point-to-point connection CP 440 Installation and Parameter Assignment
Equipment Manual, 03/2022, A5E00057742-AE 17

Only half-duplex mode can be used with an RS 485 (2-wire) setting.
Asynchronous Data Transmission
With the communication processor, serial transmission occurs asynchronously. The so-called
time base synchronism (a 󹪝xed timing code used in the transmission of a 󹪝xed character string)
is only upheld during transmission of a character. Each character to be sent is preceded by a
synchronization impulse, or start bit. The length of the start-bit transmission determines the
clock pulse. The end of the character transmission is signaled by the stop bit.
Declarations
As well as the start and stop bits, further declarations must be made between the sending and
receiving partners before serial transmission can take place. These include:
• Transmission speed (baud rate)
• Character and acknowledgment delay times
• Parity
• Number of data bits and
• Number of stop bits
Character Frame
Data is transmitted between the CP 440 and a communication partner via the serial interface in
a character frame. Two data formats are available for each character frame. 7 data bits without
a parity bit are not supported. You can set the desired format for data transmission with the
programming interface CP 440: Point-to-Point Communication, Parameter Assignment
interface.
By way of example, the 󹪝gure below shows the two data formats of the 10-bit character frame.
Basic Principles of Serial Data Transmission
2.1 Serial Transmission of a Character
Point-to-point connection CP 440 Installation and Parameter Assignment
18 Equipment Manual, 03/2022, A5E00057742-AE

GDWDELWVVWDUWELWGDWDELWVSDULW\ELWVWRSELWGDWDELWVVWDUWELWGDWDELWVVWRSELW6LJQDOVWDWHಯರ6LJQDOVWDWHಯರ6LJQDOVWDWHಯರ6LJQDOVWDWHಯರ
VWDUWELWGDWDELWVSDULW\ELWVWRSELWVWDUWELWGDWDELWVVWRSELW
Figure 2-1 10-Bit Character Frame
Character Delay Time
The 󹪝gure below shows the maximum time permitted between two characters received within
a message frame. This is known as the character delay time.
1
Signal
Time t
Character delay time
nth character ((n + 1)th character
Figure 2-2 Character Delay Time
Basic Principles of Serial Data Transmission
2.1 Serial Transmission of a Character
Point-to-point connection CP 440 Installation and Parameter Assignment
Equipment Manual, 03/2022, A5E00057742-AE 19

2.2 Transmission Procedure with a Point-to-Point Connection
Introduction
When data are transmitted, all communication partners must adhere to a 󹪝xed set of rules for
handling and implementing data tra󹪟c. The ISO has de󹪝ned a 7-layer model, which is
recognized as the basis for a worldwide standardization of transmission protocols for computer-
to-computer communication.
ISO 7-Layer Reference Model for Data Transmission
All communication partners must adhere to a 󹪝xed set of rules for handling and implementing
data tra󹪟c. Such rules are called protocols.
A protocol de󹪝nes the following:
• Operating mode
Half-duplex or full-duplex operation
• Initiative
Which communication partners can initiate data transmission and under what conditions
• Control characters
Which control characters are to be used for data transmission
• Character frame
Which character frame is to be used for data transmission
• Data backup
The data backup procedure to be used
• Character delay time
The time period within which an incoming character must be received
• Transmission speed
The baud rate in bits/s
Procedure
This is the speci󹪝c process according to which the data is transmitted.
ISO 7-Layer Reference Model
The reference model de󹪝nes the external behavior of the communication partners. Each
protocol layer, except for the lowest one, is embedded in the next one down.
Basic Principles of Serial Data Transmission
2.2 Transmission Procedure with a Point-to-Point Connection
Point-to-point connection CP 440 Installation and Parameter Assignment
20 Equipment Manual, 03/2022, A5E00057742-AE