PLC 5 1771DB to CLX

NBJamie99

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I have been asked to quote a PLC upgrade, in which the customer wishes to replace the current plc 5 processor with a RIO module, and add a new control logix rack. I believe I have most of this under control, from various searches here and on Google.

But... The existing rack has a 1771-DB module, which the customer has the DRS file for, but leads me to my question.

Q1. It appears the PLC 5 was accessing data from the 1771-DB the same way it does from an analog IO card (BTR, BTW). Would I be safe to assume that I should be able to handle this in Logix the same way as analog IO with messages?

If it makes any difference, to my knowledge the module only has a connection on the RS-232 port.

Thanks in advance.

Details: 1785-L80B processor. 1 DH+ connection, and 3 RIO channels.

If anything else is needed, I would be happy to provide it.
 
According to http://literature.rockwellautomation.com/idc/groups/literature/documents/um/1756-um514_-en-p.pdf
any 1771 module installed within a 1771-ASB controlled chassis and Universal RIO (blue-hose) linked to a 1756-DHRIO module channel set to RIO Scanner mode could be controlled by the 1756-DHRIO module resident owner CLX CPU.
Data transfer is being accomplished via RSL5K Block Transfer Type Message (MSG) instructions.
I am not aware of any 1771 Block Transfer hardware compatibility issues/restrictions; it might very well be just as easy as reading/writing to a 1771 Analog module.
 
You are on the right track; the 1771-DB block transfers run just like any other module block transfers.

The RA Knowledgebase mentions the 1771-DB specifically in a RIO adapter rack with a 1756-DHRIO scanner:

https://rockwellautomation.custhelp.com/app/answers/detail/a_id/54791 (Access Level: Everyone).

Read up carefully both here and on the RA Knowledgebase, or consult with a knowledgeable specialist before going after a PLC-5/80 migration with DHRIO modules. You can run out of block transfer and DH+ message capacity fast.
 
NBJamie99 said:
I have been asked to quote a PLC upgrade, in which the customer wishes to replace the current plc 5 processor with a RIO module, and add a new control logix rack. I believe I have most of this under control, from various searches here and on Google.

But... The existing rack has a 1771-DB module, which the customer has the DRS file for, but leads me to my question.

Q1. It appears the PLC 5 was accessing data from the 1771-DB the same way it does from an analog IO card (BTR, BTW). Would I be safe to assume that I should be able to handle this in Logix the same way as analog IO with messages?

If it makes any difference, to my knowledge the module only has a connection on the RS-232 port.

Thanks in advance.

Details: 1785-L80B processor. 1 DH+ connection, and 3 RIO channels.

If anything else is needed, I would be happy to provide it.
Click to expand...

Done this many times before , you just have to be careful and not let the message instruction run too often. Use a timer to manage when Message isntruction can run.

ScreenHunter_01 Apr. 09 20.41.jpg
 
Ken Roach said:
You are on the right track; the 1771-DB block transfers run just like any other module block transfers.

The RA Knowledgebase mentions the 1771-DB specifically in a RIO adapter rack with a 1756-DHRIO scanner:

https://rockwellautomation.custhelp.com/app/answers/detail/a_id/54791 (Access Level: Everyone).

Read up carefully both here and on the RA Knowledgebase, or consult with a knowledgeable specialist before going after a PLC-5/80 migration with DHRIO modules. You can run out of block transfer and DH+ message capacity fast.
Click to expand...

Where can I read up on the message capacity? I can not seem to find that listed anywhere. Would a controller not validate if I set one up and tested the IO layout?

Thanks
 
Do you have access to the RA Knowledgebase ? There are good articles in there about how the ControlLogix handles buffers and connections with respect to the 1756-DHRIO module, in particular Answer ID # 41853.

When quickly scoping out a project, any less than 16 block-transfer modules I will use the 1756-DHRIO. I might do more but only after examining the application closely.

Count your modules carefully and examine what sort of inter-PLC messaging is happening on DH+.
 
I do have access and will check that out when I get home, thanks. This particular application only has 9 modules that will need block transfers. To keep the existing wiring the same, I was planning to use 2 dhrio modules for 1 dh+ connection and 3 Rio channels. Not that it would effect the messaging.

Thanks again.
 
Wait are you planning on using a DHRIO or RIO module? The RIO module takes care of all the block transfers. You do not need to do any BTs yourself.
 
Even with analog modules?

I do need one dh+ connection and 3 Rio connections. So I was planning 2 dhrio modules.
 
Last edited:
Yup. That's the reason to use a RIO module. There's a utility that you use to configure the module and it takes care of the BTs. Works great but it's a little expensive. But as I've said, it works great. You will still need a DHRIO for a DH channel.
 
Last edited:
jkerekes said:
Wait are you planning on using a DHRIO or RIO module? The RIO module takes care of all the block transfers. You do not need to do any BTs yourself.
Click to expand...

Apparently the 1756-RIO module does not support block transfer type data transfer to/from a remotely (Universal RIO) "connected" 1771-DB module.
Refer to Chapter 1/Page 12 and/or Appendix C of :

http://literature.rockwellautomation.com/idc/groups/literature/documents/um/1756-um534_-en-p.pdf

for the supported legacy and FLEX hardware capable to communicate with a 1756-RIO communication module.
You could try adding the 1771-DB as a "generic" module, however, you might not be able to accomplish the task at hand and be out of $2600.
 
Last edited:
Well I did some more digging, and came to the same conclusion. I also thought that if I was looking at using 2 DHRIO modules, I might be able to use 1 of each, but do not think that would work given that the rio module only has 1 channel.

I also determined that the DHRIO module is recommended that if you are using the DH+ connection, that channel 2 should be disabled. Which drives up the number of modules needed to cover the number of existing channels. Anyone have thoughts or experiences with the this issue?

Also, at the link below is a comparison document between the 2 modules.

https://rockwellautomation.custhelp.com/app/answers/detail/a_id/70199

This is very helpful, but also says the DHRIO channels should be limited to 15 connections per channel, to maintain performance levels.

Thanks again for all the thoughts and help.
 
Yes, I should have mention that the RIO has only one channel and the DHRIO has two. If your going to use DH+ @ 230 KB, then channel 2 is disabled, If your going to use DH+ @ 57.6 KB both channels can be used.

The DHRIO module is limited in the number of racks and BTs it can handle. It isn't as good as the PLC5s built-in scanner for example. It's easy to outstrip it's capabilities.
 
You might want to see what the program in that DB card is. I did a few conversions and just did away with the db cards and uses the serial port on the plc. You could also look at a prosoft card.
 

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