Communication Processor And Modbus Tcp; Using The Serial Communication Interfaces - Siemens SIMATIC S7-1200 System Manual

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Communication processor and Modbus TCP

Two communication modules (CMs) and one communication board (CB) provide the

interface for PtP communications:

● CM 1241 RS232 (Page 1543)

● CM 1241 RS422/485 (Page 1544)

● CB 1241 RS485 (Page 1541)

You can connect up to three CMs (of any type) plus a CB for a total of four communication

interfaces. Install the CM to the left of the CPU or another CM. Install the CB on the front of

the CPU. Refer to the installation guidelines (Page 67)for information on module installation

and removal.

The serial communication interfaces have the following characteristics:

● Have an isolated port

● Support Point-to-Point protocols

● Are configured and programmed through the point-to-point communication processor

instructions

● Display transmit and receive activity by means of LEDs

● Display a diagnostic LED (CMs only)

● Are powered by the CPU: No external power connection is needed.

Refer to the technical specifications for communication interfaces (Page 1530).

LED indicators

The communication modules have three LED indicators:

● Diagnostic LED (DIAG): This LED flashes red until it is addressed by the CPU. After the

CPU powers up, it checks for CMs and addresses them. The diagnostic LED begins to

flash green. This means that the CPU has addressed the CM, but has not yet provided

the configuration to it. The CPU downloads the configuration to the configured CMs when

the program is downloaded to the CPU. After a download to the CPU, the diagnostic LED

on the communication module should be a steady green.

● Transmit LED (Tx): The transmit LED illuminates when data is being transmitted out the

communication port.

● Receive LED (Rx): This LED illuminates when data is being received by the

communication port.

The communication board provides transmit (TxD) and receive (RxD) LEDs. It has no

diagnostic LED.

S7-1200 Programmable controller

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