3964(R) Communication - Siemens SIMATIC S7-1200 System Manual

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Table of Contents

Communication processor and Modbus TCP

13.3 Point-to-point (PtP) communication

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

synchronization (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.

3964(R) communication

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).

Article number

S7-1200 Programmable controller

System Manual, V4.2, 09/2016, A5E02486680-AK