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1 x Allen-Bradley PLC5 + 1 x Digi One IAP and 4 x Modbus TCP Servers

+1 vote
We are using a Digi One IAP module as a protocol bridge between an Allen Bradley PLC5 Ethernet/IP and a remote device supporting Modbus TCP. The existing system is configured as below and works fine:
AB PLC5/40E < ---- > Digi One IAP < ---- > Modbus TCP Server
The PLC uses a message function to talk to the Digi One IAP module and treat it as a “read from SLC” function. The IAP module converts the AB Ethernet request to Modbus TCP and requests the data from the remote Modbus TCP server. The IAP module is therefore acting as a protocol bridge. The data returned from the Modbus TCP server is held in the IAP module and appears to the PLC5 as a data stored in register N10 of a remote SLC plc. The message function in the PLC5 requests data from the IAP module in N10 and returns it to the PLC5 in whatever data table has been assigned to the retrieved data. All of this works fine without a problem.
We want to expand it further by supporting multiple Modbus TCP servers (up to 4) by using a single Digi IAP module.
Using the Digi IAP module you can set a number of destinations in the routing table and in our case this is 4 Modbus TCP units with consecutive IP addresses. The problem seems to be that the Digi IAP module cannot process data from more than one of the Modbus TCP Servers. We only get data from the first unit. Ideally we either want data in N10: 0-240 as a contiguous block or we are happy with 4 separate blocks, but we cannot see a way to achieve this.
Is there a way to make 1 x Digi One IAP module to do this process or do we have to have 1 module per Modbus TCP Server.
Thanks in advance for your support.
asked Jan 9, 2016 in Modbus and Industrial Automation by mhdnaeem New to the Community (2 points)

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2 Answers

0 votes
The following knowledge base article implies this should be possible with the Digi One IAP product and gives an explanation/tips for possible issues (i.e. slave timeouts).



http://ftp1.digi.com/support/documentation/90000647_B.pdf

I do see that there is a limit of 2 Modbus TCP Servers on these units.
answered Jan 13, 2016 by userid0 Veteran of the Digi Community (2,156 points)
edited Jul 7, 2016 by userid0
You need to dive into the 'address' of PLC5 comm block. I haven't worked with this for 8 years ... but in your SLC message block, you should be able to set up some COMM info - like a slave address.

If you look here, you can see this from RSLgx-5000 view-point, but will be similar to PLC5.
http://ftp1.digi.com/support/documentation/90000643_a.pdf

Again, my old brain is fuzzy, but on the comm tab you have the 'dst link' and 'dst node' settings, which default to be treated by the IAP as Modbus address 1 (aka: your first table entry). Try putting 2, 3, and 4 into the appropriate 'dst node' ... and if memory serves me, this will cause the IAP to use each of 4 entries.

Adding - if your RSLogix MSg block offers 'local' or 'remote' addressing, pick local, as then I think it only asks a DF1-like SRC & DST info. You want the DST. The 'remote' should still work, but it is DH+like and more complex to set.
Did you forget to attach the KB link?
0 votes
(Sorry - this answer got flipped into a comment, so put it back; i'm new to this forum)

You need to dive into the 'address' of PLC5 comm block. I haven't worked with this for 8 years ... but in your SLC message block, you should be able to set up some COMM info - like a slave address.

If you look here, you can see this from RSLgx-5000 view-point, but will be similar to PLC5.
http://ftp1.digi.com/support/documentation/90000643_a.pdf

Again, my old brain is fuzzy, but on the comm tab you have the 'dst link' and 'dst node' settings, which default to be treated by the IAP as Modbus address 1 (aka: your first table entry). Try putting 2, 3, and 4 into the appropriate 'dst node' ... and if memory serves me, this will cause the IAP to use each of 4 entries.

Adding - if your RSLogix MSg block offers 'local' or 'remote' addressing, pick local, as then I think it only asks a DF1-like SRC & DST info. You want the DST. The 'remote' should still work, but it is DH+like and more complex to set.
answered Jul 7, 2016 by Coralyn Seasoned Professional (150 points)
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