Data Transmission With The 3964(R) Procedure; The Control Characters Of The 3964(R) Procedure - Siemens SIMATIC S7-400 Equipment Manual

The settings required for the different topologies can be made in the parameter assignment
interface in the "Interface" dialog box.
Note
When you run the ASCII driver in RS422 multipoint or RS485 mode, you must take steps in the
user program to ensure that only one node sends data at any one time. If two users send data
simultaneously, the message frame is corrupted.
2.5

Data Transmission with the 3964(R) Procedure

Introduction
The 3964(R) procedure controls point-to-point data exchange between the communication
processor and a communication partner. As well as the physical layer (layer 1), the 3964(R)
procedure also incorporates the data-link layer (layer 2).
3964(R) procedure startup
The figure below illustrates the startup of the 3964(R) procedure.
Power-up after restart of the
CPU or voltage recovery
Evaluate parameter assignment
Figure 2-12
2.5.1

The Control Characters of the 3964(R) Procedure

Introduction
During data transmission, the 3964(R) procedure adds control characters to the information
data (data-link layer). These control characters allow the communication partner to check
whether the data has arrived complete and without errors.
Point-to-point connection CP 440 Installation and Parameter Assignment
Equipment Manual, 03/2022, A5E00057742-AE
Initialize interface
Send NAK
G
Flow Diagram of the Startup of the 3964(R) Procedure
Basic Principles of Serial Data Transmission
2.5 Data Transmission with the 3964(R) Procedure
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