Communication
Function Manual, 11/2019, A5E03735815-AH
121
Point-to-point link
8
Functionality
A point-to-point connection for S7-1500, ET 200MP and ET 200SP is established via
communications modules (CMs) with serial interfaces (RS232, RS422 or RS485):
●
S7-1500/ET 200MP:
–
CM PtP RS232 BA
–
CM PtP RS422/485 BA
–
CM PtP RS232 HF
–
CM PtP RS422/485 HF
●
ET 200SP:
–
CM PtP
The bidirectional data exchange via a point-to-point connection works between
communications modules or third-party systems or devices capable of communication. At
least 2 communication partners are required for communication ("point-to-point"). With
RS422 and RS485, more than two communications partners are possible.
Protocols for communication via a point-to-point connection
●
Freeport protocol (also called ASCII protocol)
●
Procedure 3964(R)
●
Modbus protocol in RTU format (RTU: Remote Terminal Unit)
●
USS protocol (universal serial interface protocol)
The protocols use different layers according to the ISO/OSI reference model:
●
Freeport: Uses layer 1 (physical layer)
●
3964 (R), USS and Modbus: Use layer 1 and 2 (physical layer and data link layer;
therefore greater transmission reliability than with Freeport). USS and Modbus use
additionally layer 4.
Properties of the Freeport protocol
●
The recipient recognizes the end of the data transfer by means of a selectable end
criterion (e.g. character delay time elapsed, receipt of end character, receipt of a fixed
amount of data).
●
The sender cannot recognize whether the sent data arrived free of errors at the recipient.
Summary of Contents for SIMATIC ET 200SP
Page 1: ...Communication ...
