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Connecting two MPI adapter to one PLC


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#1 PLCMania

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Posted 14 January 2006 - 06:17 AM

Hi,
I have a touch panel connected to an S7-300 PLC via SIEMENS serial MPI adapter. I want to connect my PC via another USB MPI-Adapter to the same PLC.
The serial MPI-Adapter is operating OK and is always Online, but when I try to get the status of a block in PLC from PC, it comes no response from PLC and the USB MPI-Adapter hangs.
I checked the address of both Adapters and are different.
I used the command "accesssible nodes" from PC and I see the MPI address of Serial MPI-Adapter and the PLC.
Any sugesstons?
Thanks

#2 JesperMP

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Posted 14 January 2006 - 01:02 PM

It is possible that the problem is electrical.

A PC adapter is a droplink on the normally daisychained MPI or Profibus network.
A droplink is normally not allowed on an RS485 network, but it seems to works anyway with just one connected to one port.
To connect two one the same port may be too much.

Both the serial and the USB PC adapter needs 24VDC from the PG port. That both adapters works (more or less) seems to indicate that the problem is not related to the supply to the adapters though.

I dont see any easy solution to the problem. If there are more than one PLC on the network then you could attach each adapter to its own PLC.
An OP does normally not have 24V in its MPI/Profibus port.

#3 PLCMania

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Posted 15 January 2006 - 02:37 AM

Hi JasperMP,
As I wrote, there is only one PLC and the PC that is connected through USB MPI-Adapter to MPI Network shows the "accessible nodes" using SIMATIC Manager. That includes the MPI address of Serial MPI-Ad. and the address of PLC.
Any idea?

#4 JesperMP

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Posted 15 January 2006 - 01:04 PM

One way could be to add 2 Profibus cables via Profibus connectors.
In each of the 2 "ends" of the MPI network you have to add connectors with 5V (for the termination) and 24V (for the adapters). You could then attach a PC adapter to each one of the ends of the network.
I dont remember offhand which pins have the 5V and 24V respectively.
It sounds like a cludge though.

A neater solution could be to use a CP5611 card (PCI) installed in one of the PCs that you have connected.
The CP5611 dont need to tap 24V from the PG port. It is only a bit more expensive than a PC adapter.
Drop the awful serial adapter and exchange it with the much more powerful CP5611.

edit: Oh I see that the seral adapter is used for a touch panel.
If the PC is a laptop, then the solution is a CP5511 or CP5512 card (PCMCIA). Both dont need 24VDC from the PLC port.

Or, simply disconnect the HMI panel when you go online with the PC.

Edited by JesperMP, 15 January 2006 - 01:07 PM.


#5 PLCMania

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Posted 16 January 2006 - 06:58 AM

Hi JasperMP,
I use a Noteook as programmer and I'm not so rich to buy a CP5511 too.
I have the pinout of the MPI-Adpter and have tested it with external +24 and +5V, but no success.
there are two pins on MPI adapter and MPI interface of CPU. One is RTSAS and the other one is RTS_PG. I think the problem is due to these pins.
This is from MPI-Adapter manual:

RTS_AS: RTSAS control signal for receive data current. The signal is active ‘1’ when the directly connected AS is transmitting.

RTS_PG: Adapter’s RTS output signal. The signal is ‘1’ when the adapter is transmitting.

I solved the problem as follows:
The CPU, I'm trying to connect to, is a 313-2DP. I used the DP interface to connect the PC MP-Adapter and the touch pannel is connected through MPI port to CPU .

Thanks for you interest and replies.

#6 jacekd

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Posted 18 January 2006 - 03:21 AM

Take one DB9 male connector and two DB9 female. Make 1 to 1 connections with wires from male one to female ones for all pins.
It should do the trick.
Regards,

jacekd

#7 PLCMania

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Posted 23 January 2006 - 12:50 AM

Hi jacked,
I tested it. As I wrote, It doesn't work. :helpme: :-2




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