Basic Principles Of Serial Data Transmission; Serial Transmission Of A Character - Siemens SIMATIC S7-400 Equipment Manual

Basic Principles of Serial Data Transmission

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 fixed order.
Drivers for Bidirectional Data Traffic
The CP 440 itself handles data transmission with communication partners via its serial interface.
The CP 440 is equipped with two different drivers for this purpose.
Bidirectional data traffic:
• ASCII driver
• 3964(R) procedure
The CP 440 executes data transfer via the serial interface depending on the selected driver.
Bidirectional Data Traffic - Operating Modes
The CP 440 has two operating modes for bidirectional data traffic:
• 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 flow 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
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