PLC+TP+PG through MPI

Hello,

PLC is simatic s7-300, TP is simatic TP270, PG is PC with mpi/usb adapter.

I know i can connect all 3 devices through MPI connecter with PG socket, but my local siemens rep. wont take orders less than 1000 euros so it's impossible to buy such connector now, so i'm wondering what is the schematic of that connector?

can I do such connector by myself?

what if I just get 3 usual 9-pin connectors

and connect like 1in - 2out, will it work?

how about some sort of end-resistor?

thanks

but my local siemens rep. wont take orders less than 1000 euros

Click to expand...

I smell a lot of unexplored business opportunities here. Jeez...

Girevic

You can just use the standard 9 pin connectors, the two pins used are pin 3 and pin 8 when connected using the two wire purple 'profibus' cable. I am not sure of the value for the end of line resistor though and for some reason the Siemens support web site search engine seems to be down.

Paul

I thought he said MPI, that is 2-2, 3-3, and 5-5 isnt it? Doesnt MPI stand for multipoint protocol?

Here is pinout for Profibus/MPI connector in S7 PLC's:
1 - chassis 24V reference
3 - data line B (RxD/TxD - P)
4 - RTS (Request to Send - used by PG)
5 - data reference potential (connect it to cable shield)
6 - +5V supply for terminating resistors
7 - 24V supply for devices like TS Adapter or PC adapter
8 - data line A (RxD/TxD - N)

Terminating resistors:
390 ohm between pins 6 and 3
220 ohm between pins 3 and 8
390 ohm between pins 8 and 5.

Normally stations are conneceted with 2-wire shielded cable connected to pins 3 and 8. Cable shield is connected to pin 5 and connector shield at every connector. Cable impedance should be about 150 ohm.
Remeber that USB PC adapter probably does not provide supply for terminating resistors and may require 24V supply from PLC.
Additional signals are evaluated by PG to ensure type of connection to PLC: direct/network line.
If Siemens won't sell you connectors you may look for products from VIPA, WAGO, Phoenix Contact. They offer these connectors too. Look at their websites.

rsdoran said:

I thought he said MPI, .....SNIP..... Doesnt MPI stand for multipoint protocol?

Click to expand...

He did say that and it does stand for that, well nearly, it's 'Multi-Point Interface'

Regardless of what the other pins do he only needs to use pins 3 and 8, when I run my MPI networks (including to a PG) I use the purple 'profibus' cable which has two cores, thus only pins 3 and 8 are used, these are the mimimum pins connected he would need to get his network up and running, as stated by gregoryg

Paul

PLucas said:

Regardless of what the other pins do he only needs to use pins 3 and 8, ... thus only pins 3 and 8 are used, these are the mimimum pins connected he would need to get his network up and running, ...

Click to expand...

He needs to connect a few more pins. The USB/MPI adapter needs 24V from the PLCs MPI port. So he also have to connect pins 1 and 7.
If this are just a short connections with a few meters at 187,5 kbaud, then dont worry about the terminating resistors.

thank you guys alot! all your advices are very helpful!

so if i understand it the right way:

for a successful connection between PLC and PG (mpi/usb adapter) I need to connect 1, 3, 7, 8 pins.

and I only need 3 and 8 pins for connection between the PLC and HMI.

and i should not use any resistors since the total length of the cables will be no more than few meters...

Is this right?

and for just a few meters, do I still need profibus cable or any cable like cables from any rs232 devices (something similar to what i have in my mpi/usb adapter on the PLCs side) would be ok?


thanks again!

To your 1st question: Yes you are correct.

To your 2nd question: Try with "normal" screened cable and see how it goes. There is a nasty problem with using a real Profibus cable. It is near-impossible to solder the thin single-strand wires onto the pins in the serial connector. I have tried it, and despite it looked OK it came loose after some time.

thank you again, Jesper!

JesperMP said:

The USB/MPI adapter needs 24V from the PLCs MPI port.

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There are times Jesper, when I think I should read posts a bit more carefully, as girevic mentioned 'PG', I automatically assumed that he had a Siemens PG, I didn't notice the bit about the USB/MPI adaptor.

No problem though, you are always here to put me right!

Paul