Cable order No. 7XV5100-4 is modified RS232 cable:
DB9 connectors, female on PC-end, male on relay end;
lines between pins 2 and 3 (RxD, TxD) crossed, pins 5 (Gnd) connected straight and to the screen of cable
on PC-end: bridge between pins 4 and 6, bridge between pins 7 and 8
on relay end: bridge between pins 7 and 8
No reason to pay 50 EUR for this cable, it is very easy to solder one yourself from materials for less than 2 EUR.
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It may be like this in theory and practice, but in real life it is completely different.
The favourite sentence of my army sergeant