Is Profibus DP a real RS-485 ?

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Thread Starter

claudio

Dear Fellows, I have a simple and stupid question. All the vendors literature refers the Profibus DP as RS485 (physical level ). I will interface a CP5611 Siemens Card to a S7/300 PLC, via 342-5 Profibus DP board, on a point-to-point architecture. The communication rate I will use is 9.6 Kbps or 19.2 Kbps. Because many reasons the link must be fiberotics ( between the PC and the PLC ), but the Siemens OLM interface is deadly expensive. To connect RS485-Fiber-RS485 I usually use a normal RS485 to FiberOtics converter in both side. In the case of Profibus DP can I use a standard RS485 to Fiber converter ? In other words is profibus DP physical protocol level an RS485 ? Thanks Claudio Torres [email protected]
 
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David Bergeron

The answer is yes. Profibus over copper is RS-485. You can use an RS-485 to Fiber convertor on both ends.
 
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Rob Hulsebos

>To connect RS485-Fiber-RS485 I usually use a normal RS485 to FiberOtics >converter in both side. In the case of Profibus DP can I use a standard >RS485 to Fiber converter ? > >In other words is profibus DP physical protocol level an RS485 ? Yes it is. But: it is 2-wire RS485. There is also a 4-wire RS485 (sometimes mistakenly called RS422 by several vendors). Your converter must be a 2-wire RS485 too, and be able to work without RTS signalling the direction (L->R or R->L). If not, you're in trouble. Sincerely Rob Hulsebos
 
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