Hi,
there’s no special transfer mode in PP21.
Normally, a transfer shoud be possible with every node switch setting between 01 - FE (FF is reserved for Diagnosis mode where no transfer is possible, 00 is reserved for dedicated transfer of AR in BTL mode).
I’m really wondering about the wmpty PP21, where you wrote that AR transfer in BTL mode was possible → I agree that this would mean that the cable is ok.
But if only AR was transferred and nothing more, no special setting on the RS232 interface should be active. That means, an online connection should be possible with the default settings of 57600 Baud, parity Even, 8 Databits, 1 Stopbit with node number switch setting 01.
On the PP21 including a program, the setting of the RS232 interface can be different or even disabled, that depends on the project setup used inside the panels software project and cannot be influenced or changed.
So, unfortunately it’s hard to say what to try next.
Some time ago, I created a post with a small RUC script that should support determining the RS232 settings.
Please have a look here, maybe it helps:
Best regards!