Talking to two devices, at the same time.

[MimiKLM]

That is it!

Many thanks Albert.

So just for explanation, what is the difference between sending *STB? via write and STB VI?

[Albert.Geven]

The function works in the gpib interface. The *STB works via the next level higher.

The function only returns a byte directly on the bus. The *STB string has to be interpreted in the machine and then a byte has to be returned.

Nice that you saw it works.

[MimiKLM]

Albert,

But generally, how to get know what functions work in the GPIB interface and which function work on the next level higher?

There is no a lot of explanations in the LV help.

[Albert.Geven]

This is the only function that works at the chip level.
It is very specific for gpib and I understand why it is not documented. It is too low level.
In fact it is a pity that the other command also exists, because it is not needed.