Answer / carl_ellis

The Profibus DP specification defines the hardware transport
physical layer as 2 wire RS-485. The communications
protocol and the transport layer are both part of the
Profibus DP specification (the separate 2 wire cable for
24Vdc power supply is not involved with the communications).

Any device that passes Profibus DP certification will
conform to the Profibus DP specification.

Therefore, a 4 wire RS-485 device will not work on a
Profibus DP network because it won't be a Profibus DP
device, it does not meet the Profibus DP spec, which is 2
wire RS-485.

Attempting to operate a 4 wire RS-485 device on a Profibus
DP network will only disrupt Profibus DP communications on
the network.

Carl Ellis
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