Peer Link is a super easy way to share data between any combination of Do-more enabled
PLCs and DirectLogic PLCs that have ecomm100 cards.
Each PLC in the network has a copy of the shared PEERLINK memory. And each PLC can write
to some portion of that shared memory space that it owns. We call that publishing data.
When a PLC writes to its portion of the peer link memory space, everyone can see it as
if it just another block of local memory. And it�s so easy to use. You just drop a
PEERLINK instruction on a rung, select which blocks of the shared memory this PLC owns
and you�re done. Each block has 16 PL memory locations so there are a total of 256 PL Memory
locations. This is an asynchronous instruction so as
long as it is enabled it will update the PL memory space.
The only catch is peer link uses TCP broadcast messages so all the PLCs that are sharing
this PEERLINK memory space have to be on the same local TCP broadcast domain. Which means
they all have to be on the same local network and not behind a router.
I have a local network that my PC is on with this IP Address, so let�s add this PLC to
that network at dot 59. Configure. Configure. And change the IP Address so it is compatible
with the network. Let�s have this PLC increment PL0 once a
second � remember we gave this PLC access to the first four blocks of Peer Link memory,
so it can write � or publish data - to locations zero through 63.
Accept our changes and write it out to the PLC. Make sure the PLC is in RUN mode and
with status enable we can see which blocks of the peer link memory space this PLC is
publishing to and that there is no activity in the other blocks. Great.
Let�s disconnect from this 36 point BRX PLC and connect to an 18 point BRX PLC. I
connected to the 36 point BRX PLC via USB. Now I want to connect to the 18 point BRX
PLC via Ethernet, but I have no idea what his current IP Address is. All I know is I
want him to be compatible with my new network. How to I fix that? Easy. If you go to this
NetEdit utility and select the Ethernet adapter you want to use � I have several on this
PC so we want the one that�s on our network � I see the IP Address of the 18 point BRX
PLC, is this. Let�s change that to our network dot 58 so it can talk to everyone on our network.
Now that he is on our network, let�s connect to him. I don�t have a link to this guy
yet, so let�s add one. We know it�s connected via Ethernet, make sure we are using the right
adapter, and sure enough there�s Mr. dot 58. Let�s give him a name, and I�ll note
that it�s an Ethernet connected PLC. Now we can select that guy and connect to him.
We know he is different than what we had before and we know we need to write the new program
before it will take effect. Let�s have him control these four blocks of shared Peer Link
Memory. Let�s have this guy take the data published
by the first PLC, double it, and publish it to the last memory location this PLC has access
to. Accept. And write it out to the BRX PLC. If
we put this PLC in RUN mode and enable status we can see this PLC is controlling these outlined
blocks and someone else is controlling these blocks. Everything is green which means everyone
is on-line and operating normally. If we bring up a data view, we can see what
the first PLC is doing to its section of the PEERLINK memory and what this PLC is doing
to its section. How cool is that � we can see what the other PLC is doing and we didn�t
have to do anything except add a PEERLINK instruction to this PLC. Very cool.
Let�s add one more PLC to our PEERLINK network� how about the simulator. Disconnect from the
18 point BRX PLC. And connect to the simulator. Its telling me the simulator is not in terminal
mode so let�s bring it on the screen, switch it to terminal mode and move it back out of
the way again. Yes we know it�s a different PLC and yes
we know things have changed and we need to write them to the PLC to take effect. Fine.
We don�t really care about the clock or the configuration right now. Let�s have
this 3rd PLC control these five blocks of the shared PEERLINK memory space. We know
that going to be a problem because the last PLC we setup is controlling these blocks.
Right? But let�s do it anyway and see what happens.
What about the Ethernet address of this simulated PLC? Well, remember, this is the simulator.
It�s really in the PC and uses the PC�s Ethernet port as its IP address so we can�t
change that. That�s why I setup this network to be compatible with my pc � So we could
use the simulator. Great. Accept all of that. Write it to the
PLC. Make sure the PLC is in RUN mode and enable status. Ahh! Look at that. This PLC
is trying to control these 5 blocks of memory, but there is conflict with this block � someone
else is trying to use it! We know that, so let�s change this PLC to use these 5 blocks.
Accept it, write it out � and voila! Everybody is happy again.
And look. This PLC can see what the other two PLCs are doing. And if this PLC publishes
data to its PEERLINK memory, the other PLCs will be able to see that. So now you have
a quick and easy way to share data between any combination of Do-more and DirectLogic
PLCs. Peer link is updated about 10 times a second
as long as the instruction is enabled. And look at this � there�s all kinds of
status bits you can use. If we take this one and switch it to binary � the ones tell
us which blocks are active. Then for each block � let�s look at block 0 � You
can tell if the block is being used, if there are any errors, what the current update rate
is and if it has been updated recently. And, you can inhibit a block if you want to
take tit off the PEERLINK network. So peer link is a super quick and easy way
to share up to 256 memory locations between an assortment of Do-more or Direct Logic PLCs.
You just drop the Peerlink instruction in place, enable it and make sure the PLC is
on the right network. And it can now see the 256 PL memory locations that everyone on the
same network is sharing. A couple things to keep in mind:
The Peerlink instruction has to be in the MAIN program loop.
You can only have ONE PeerLink instruction per PLC.