Example: Point-To-Point Communication - Siemens SIMATIC S7-1200 System Manual

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Communication processor and Modbus TCP

13.3 Point-to-point (PtP) communication

Example: Point-to-Point communication

In this example, an S7-1200 CPU communicates to a PC with a terminal emulator through a

CM 1241 RS232 module. The point-to-point configuration and STEP 7 program in this

example illustrate how the CPU can receive a message from the PC and echo the message

back to the PC.

You must connect the communication interface of the CM 1241 RS232 module to the RS232

interface of the PC, which is normally COM1. Because both of these ports are Data Terminal

Equipment (DTE), you must switch the receive and transmit pins (2 and 3) when connecting

the two ports, which you can accomplish by either of the following methods:

● Use a NULL modem adapter to swap pins 2 and 3 together with a standard RS232 cable.

● Use a NULL modem cable, which already has pins 2 and 3 swapped. You can usually

identify a NULL modem cable as one with two female 9-pin D connector ends.

S7-1200 Programmable controller

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