Communication processor and Modbus TCP
13.3 Point-to-point (PtP) communication
S7-1200 Programmable controller
1092 System Manual, V4.2, 09/2016, A5E02486680-AK
Note
CM module firmware version requirement for Time synchronization and PtP communication
If you
have enabled "CPU synchronizes the modules of the device" in the Time
(Page 181) properties for the Profinet interface in the device configuration,
update the firmware versions of the connected communication modules to the latest
available versions. Enabling module time synchronization for communication modules with
old firmware versions can cause communication issues or errors.
The S7-1200 CPU supports the 3964(R) protocol to enable communication between a
CM 1241 RS232 module or a CM 1241 (RS422/485) module and a communication partner
that uses the 3964(R) protocol. Unlike the PtP communication described above where you
define specific send (transmit) and receive characteristics for the messages, the 3964(R)
protocol proscribes a strict protocol using the following control characters:
● STX Start of text
Start of character string to be transmitted
● DLE Data Link Escape
Data transmission switchover
● ETX End of Text
End of character string to be transmitted
● BCC Block check character
● NAK Negative Acknowledge
Refer to the chapter describing serial data transmission principles in the S7-300 CP 341
Point-to-Point Communication, Installation, and Parameter Assignment Manual.
(https://support.industry.siemens.com/cs/us/en/view/1117397) manual for a complete
description of the protocol.
Configuring the communication module
To communicate to a partner using the 3964(R) protocol, you must include one of the
following communication modules in your device configuration in STEP 7:
● CM 1241 (RS232)
● CM 1241 (RS422/485)
The firmware version of the CM module must be V2.2.0 or later.
For the communication module, you then configure the communication ports (Page 1093),
priority, and protocol parameters (Page 1106).
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