Siemens SIMATIC S7-400 CP 440 Installation And Parameter Assignment page 59

Point-to-point connection

Table of Contents

4. Check:

Always monitor the TXD send and RXD receive LEDs during the following operations

Example 1: The polarity of the line is definitely correct

– The default settings (all options) vary

– Check the security word (e.g. CRC)

Example 2: The default settings are definitely correct

– Reverse the connections (note: cross both pairs of lines in the RS422)

– Check the security word (e.g. CRC)

Example 3: Neither correct polarity nor correct default settings known

– Reverse the connections (note: cross both pairs of lines in the RS422)

– If not OK, change the default settings (all options) with an appropriate communication

– If not OK, change the connections back, and change the default settings (all options)

– Check the security word (e.g. CRC)

When setting up again, don't forget to put back the terminating resistors you removed.

5. Additional tips:

– If possible, connect an interface tester (possibly the V.24 → RS22/485 converter) to

– Check the signal level using a measuring device (measure level to GND - pin 8).

– Some devices do not signal reception if data is being received but the CRC security

– If necessary, replace the module to exclude the possibility of an electrical defect.