What is difference between profibus dp and profibus pa?

First I think I should point out that Profibus-PA instruments do not use RS-485 (such as is used by Profibus-DP), but a MBP (Manchester Coded, Bus Powered) physical layer, as described in the IEC 61158-2 standard.

This is why you need a bus coupler to 'translate' the signals from Profibus-DP to Profibus-PA, and to power the PA bus.

The maximum transmission rate of Profibus DP network 12Mbps

The maximum transmission rate of Profibus PA network 45.45Kbps

You need to power the DP instruments, while PA instruments get its power and exchange data via the same PA cable .

You need DP/PA link or DP/PA coupler to link DP network with PA .

when you use a coupler connected directly to the DP network , then your DP network transmission rate would be decreased to 45.45.

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Pradip