x_send and x_rcv

Hi!
I have a problem understanding the parameters for the following functions x_send and x_rcv in Step 7
I need transfering 4 DB from one PLC to another constantly. What is the menanig of the Req_id?

REQ_ID is just an identification of the communications job at hand. You cannot use 0 for this parameter, because X_RCV would think there is nothing to wait for. REQ_ID has to be te same value on both X_SEND and X_RCV. In this way you can transfer various messages on one and the same cable, without interference.

Suppose you have 4 PLC's (PLC1 to PLC4) and PLC1 has something to send to PLC2 and PLC3 and PLC4 is sending to PLC1. You can then set up communications as follows:

PLC A   Function   REQ_ID   PLC B   Function   REQ_ID

PLC1     X_SEND      1      PLC2     X_RCV       1

PLC1     X_SEND      2      PLC3     X_RCV       2

PLC1     X_RCV       3      PLC4     X_SEND      3

Hope this helps.
Kind regards,

Thanks, that was helpful!
But i have little question more...
Why is the Req_id on the x_rcv as an output parameter, so i cannot input the value (the number of the request that is the same that in the x_send? )

Because everything is sent to every PLC on the cable. In the receiving you have to check if the received REQ_ID is the right one before you use the received data.

The sending PLC sets the REQ_ID to a certain value, the receiving PLC checks to see if the received communication has the right REQ_ID.

Kind regards,