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

Communication processor and Modbus TCP
12.3 Point-to-point (PtP) communication
12.3.5

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.
704
S7-1200 Programmable controller
System Manual, 03/2014, A5E02486680-AG