DP/DP coupler - help needed

Cryogen · Nov 15, 2006

Hi Everyone,

We recently shipped a siemens S7-200 (CPU 224XP) PLC with a profibus module EM277 as customer wanted to connect our PLC (through the EM277) to their profibus network.

The EM277 can only be used as a slave. Our customer is trying to connect it to a DP/DP coupler. Is this even possible? Can a slave be connected to the DP/DP coupler. I thought the DP/DP coupler is to connect two masters together. He mentions it is used to amplify the signal as the distance is long and that it can be connected to a slabe. He wants us to change some configuration on our end..

For those of you who know the EM277, there isn't anything in that that can be changed.. We just let them know the bits of data.. Even the address is user changeable. So I am stuck... Please let me know if there is anyway this can be connected to a DP/DP coupler.

Thanks..

PeterW · Nov 15, 2006

He appears to have mixed up a repeater and a DP Coupler.

You are correct DP Couplers need assigning in the hardware config.

Repeaters are invisible to the system.

Cryogen · Nov 16, 2006

Thanks for your reply.

So is the purpose of connecting DP/DP coupler only to connect two masters together?

PeterW · Nov 16, 2006

Cryogen · Nov 16, 2006

Thanks again..

dchartier · Nov 16, 2006

Hello Cryogen;

Yes the DP/DP coupler is only to connect 2 masters on a DP network. It has 2 DP interfaces, each one configured as a slave by a different master.
Whatever data the first master writes to its DP/DP coupler slave can be read by the second master, and vice-versa.
Hope this helps,
Daniel Chartier

Ken M · Nov 16, 2006

Just to nit-pick and split hairs slightly, the purpose of a DP/DP Coupler is to provide a connection point between two networks, not to connect on two masters on a single network.

The two networks on either side of the DP/DP Coupler remain quite independent. If you connect Master A's network with 3 slaves to Master B's network with 4 slaves you don't have to reconfigure either master for 8 slaves total (3 + 4 + DP/DP Coupler). Master A is entirely unaware of B's own 4 slaves and doesn't have to (mustn't!) include these in token rotation calculations, and vice versa. If you did have a single network with dual masters then both masters would have to take account of every slave's presence whether they 'owned' it or not.

There. I bet you feel a lot better knowing that.

Ken

dchartier · Nov 16, 2006

There. I bet you feel a lot better knowing that.

Thanks Ken. I know I do.
And thanks for the detailed info. Really much appreciated.
Daniel Chartier

PeterW · Nov 16, 2006

Ken M said:
not to connect on two masters on a single network.

I answered yes to 'So is the purpose of connecting DP/DP coupler only to connect two masters together?'

no mention of single network.

nit-picking again

Ken M · Nov 16, 2006

I wasn't actually aiming my nit-pick or hair-split at Daniel or anyone else. The mark of the true nit-picker is that he would probably write the correction (as he sees it) even if there were no audience to read it! It's the pedantic display of useless information that matters. That's where they get their satisfaction.

Ken

L D[AR2P#0.0] · Nov 16, 2006

I'm presuming you could connect both sides of the DP coupler to the same network and then one master would have two slaves. Why ? well you might want to test the interface before the two masters were physically available.

PeterW · Nov 16, 2006

L D[AR2 said:
I'm presuming you could connect both sides of the DP coupler to the same network and then one master would have two slaves. Why ? well you might want to test the interface before the two masters were physically available.

Why? it's like connecting inputs to outputs and vice versa. A simple interconnection between two PLC's which needs no comms software.

The DP on the hardware config is a an I/O point, just the same as having a small rack where you can insert groups of I/O.

The partner PLC is the same, you just have to match the patterns, if your first word is an input on one, its an output on the other.

EDIT: sorry just re-read your post.

There are two DP networks, the PLC's are master of their own. Each network can have the usual mixture of devices attached. The DP coupler is just another slave attached, each PLC only see's their side. One PLC cannot see any slave the other side of the DP.

Ken M · Nov 16, 2006

OK, I've completely missed the point of this one!

What an weird idea this is (connecting both ports to the same network and master). So the PLC would be reading input data from Slave 1 (which of course had come from Output data in Slave 2) and writing Output data to Slave 1 (which of course would appear as input data from Slave 2) and reading input data from Slave 2 (which of course had come from Output data in Slave 1) and writing Output data to Slave 2 (which of course would appear as input data from Slave 1). Of course you've got to configure both slaves and write some code to move values around to see that they change. And the purpose is to test it (the Coupler)? I'd rather just power it up and see if it got warm. That's as good a test as any. I've honestly never known a DP Coupler to fail. They just sit there doing their stuff. Excellent little devices.

Regards

Ken

L D[AR2P#0.0] · Nov 16, 2006

I threw this in to demonstrate that a coupler is after all just two slaves. Maybe one day someone might need some extra flags so you could add the coupler as a mechanism for storing data (that isn't in a DB) - just keeping all options open !

Ken M · Nov 17, 2006

Two slaves, two networks... I guess one man's Coupler is another man's Separator

(But how does a Coupler give you more data storage? It's your own IO you're using to address it after all. Why not just write/read unconfigured outputs and save the cost of a Separator?)

Ken

DP/DP coupler - help needed

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