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

Communication processor and Modbus TCP

12.1

Using the serial communication interfaces

Two communication modules (CMs) and one communication board (CB) provide the
interface for PtP communications:
● CM 1241 RS232 (Page 975)
● CM 1241 RS422/485 (Page 976)
● CB 1241 RS485 (Page 973)
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" chapter in the S7-1200 System Manual (Page 62) for
detailed instructions 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
● 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 964).
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
● Transmit LED (Tx): The transmit LED illuminates when data is being transmitted out the
● Receive LED (Rx): This LED illuminates when data is being received by the
The communication board provides transmit (TxD) and receive (RxD) LEDs. It has no
diagnostic LED.
S7-1200 Programmable controller
System Manual, 03/2014, A5E02486680-AG
instructions
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.
communication port.
communication port.
12
669