Siemens USB/MPI+ and Profibus communication

Hello everyone,
I have S7-300 PLC connected to HMI pannel with Profibus. I bought a USB/MPI+ cable from ebay, now this cable does not support profibus, so i can not just connect it to profibus cable at my HMI pannel I have to go all the way to PLC unplug the profibus connector and then directly connect the USB/MPI+ cable. Is there a work around or a modification that i can do to the USB/MPI+ cable to make it work with profibus?


your help is greatly appreciated.

Thank you

Is this a genuine siemens cable or clone?

if it is siemen's - whats the part number?

definitely not genuine, its a clone, but it is using the same drivers though.
Hardware version 1.0 and Firmware version 1.2

I've never used any chinese interface, but all the german clone interfaces match functionality 100% so support Profibus and can be externally powered so you can plug into the network anywhere.

Looks like your Interface is MPI only.

I guess it is, can you recommend any german clones? basically i'm looking for something cheaper than the original, dont feel like spending $500 on the cable.

but it must have something to do with getting power, i'm not familiar with how the MPI cable is wired but I know that the profibus is only 2 wires and i dont think they provide power to the cable.

zer0net said:

I guess it is, can you recommend any german clones? basically i'm looking for something cheaper than the original, dont feel like spending $500 on the cable.

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I use an IBH netlink - Ethernet to MPI/Profibus on non PN Cpu's
http://www.ibhsoftec-sps.de/english/Selection_Hardware_S7.htm

Prior to that i have used USB/Serial interfaces from
Systeme Helmholz,process-informatik & MHJ which i think are all basically the same.

zer0net said:

but it must have something to do with getting power, i'm not familiar with how the MPI cable is wired but I know that the profibus is only 2 wires and i dont think they provide power to the cable.

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I think its more likely the interface board - the adaptors i've mentioned all support MPI/Profibus but don't use the Bus cable you mentioned.

Geniusintraining a member here sells the interface i think you have, so would be able to better advise.
Website: http://www.plctrainer.net/PLCProgrammingCables.htm

Have you tried it in the CPU DP port with PC adaptor interface in set PG/PC interface set to Auto?

STL??? said:

Have you tried it in the CPU DP port with PC adaptor interface in set PG/PC interface set to Auto?

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Yes I have, It works fine when directly connected to PLC just doesnt work if i connect it to the profibus at the HMI end or profibus connector connected to PLC (the profibus connectors I have are dual port, one end you can connect to something and you can connect something else behind it)

Yes I have, It works fine when directly connected to PLC just doesnt work if i connect it to the profibus at the HMI end or profibus connector connected to PLC (the profibus connectors I have are dual port, one end you can connect to something and you can connect something else behind it)

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Right - bottom line you need either an aftermarket adaptor with external voltage capability or siemens wise CP5511/12 pcmcia or CP5711.

At a node or HMI you simply have no power for your adaptor.