Siemens SIMATIC CP 440 Manual page 26

Basic Principles of Serial Data Transmission
Transmission Integrity
Transmission integrity plays an important role in the transmission of data and in
selection of the transmission procedure. Generally speaking, the more layers of the
reference model are applied, the greater the transmission integrity.
Classifying the Supplied Protocols
The CP 440 can handle the following protocols:
ASCII driver
3964(R) procedure
The figure below illustrates how these protocols of the CP 440 fit into the ISO
reference model:
Layer 2
Layer 1
Figure 2-3
2-8
Data link layer
The data bytes are transmitted with
3964(R). Start and stop bits are added;
in the event of an error the transmission
may be repeated.
Physical layer
The physical transmission of the
data bytes is defined.
How the Protocols of the CP 440 Fit into the ISO Reference Model
Point-to-point connection CP 440 Installation and Parameter Assignment
A5E00057742-02