SLC 5/05 with remote I/O & analog

My local AB tech guy insists that I must use block transfers with an analog module in a remote rack. I believe that he may be wrong.
This was a rack with a CPU which is being changed to a remote rack, which brings up the analog addressing problem.
I don't have an analog module to test right now but......

On the bench I have set up the following:
Local rack:
slot #0 is SLC 5/05
slot #4 is 1747-SN

Remote rack:
slot #0 is 1747-ASB
slot #1 is 1746-IB16
slot #2 will be 1746-NIO4I (2 analog inputs and 2 analog outputs)
slot #3 is 1746-IA16
slot #4 is 1746-IA16
slot #5 is 1746-OA16
I have set up the remote rack as 1/2 slot which gives two words per slot.
slot #1 input addresses begin at I:4.0/0
slot #3 input addresses begin at I:4.4/0
slot #5 output addresses begin at O:4.8/0
This works on the bench (for the discrete I/O modules)so I would expect the analog output addresses for slot #2 to be:
first output O:4.2
second output O:4.3

Will this work? I really would like to avoid using block transfers.

I realize that if I was using a four-channel analog module ( four inputs or four outputs) that I might have to leave some slots vacant.

Thanks in advance for any help.

Welcome to the forums!

What makes you think the AB tech is wrong? You say that you EXPECT RIO analog addressing to work the same as RIO discrete addressing, did you ask the AB tech if your expectation is reality? Did you read the manuals to see if this was true?

Analog RIO addressing does not operate in the same manner as discrete addressing, so yes you do need to use block transfers. Block transfers aren't that bad if you do some homework, but if you set them up wrong your analog IO won't work properly and it could had adverse affects on your discrete IO.

Reality check - just say no to block transfers

"What makes you think the AB tech is wrong?"

"did you ask the AB tech if your expectation is reality?

" Did you read the manuals to see if this was true?"

OK I think I understand "if the AB guy says it is so, then it must be so".
Perhaps hudreds of hours on the phone with AB and Rockwell over the years has lowered my expectations.

I don't expect the AB guy to know all of the details of AB PLC land. Especially for Remote I/O which might be considered to be almost obsolete.

I have all of the installation and user manuals and have bothered to read them. By reading them again today I found the following in the 1747-ASB user manual beginning on page 3-11:


"When the 1747-ASB module is configured for 1/2-slot addressing, you can use 4-, 8-, 16-, 32-point, discrete combination and specialty I/O modules in any slot. If the discrete mode is selected, specialty modules with four words or less of input or output image are discretely mapped such as the 1746-NI4, -NO4I, -NO4V, and -HS. However, with a specialty module such as the 1746-HS, the adjacent slot must be empty. Specialty modules with more than four words of input or output image are block transfer mapped such as the 1746-BAS".

This seems to make it clear that what I was trying to do in discrete mode is OK with AB.

That it is not OK with my AB tech guy is just one of life's little lessons. Thanks for trying anyway.


I will not have access to a 1746-NIO4I module until I get to the factory.

I have today tried a 1746-NO4I module (4 analog outputs) using 1/2 slot addressing and discrete mode and it works just as the manual says it should.
And no block transfers.

I'm happy that you have found a solution without using block transfers. My apology's for striking a nerve.

Usually first posts are of these flavors:
1 - Give me the answer to my homework.
2 - Do my work for me.
3 - Valid questions that sometimes lack details.
4 - Great questions with details needed for a direct answer.

I posed valid questions too you to better understand how you came to the conclusion about your rep, and to get more details from you. If you would have quoted the manual originally I would have agreed with your conclusion.

I have always used block transfers for analog IO as I was not taught any "exceptions", even if I was made aware of those exceptions I would still use block transfers to maintain consistency in my programming style, but that is just me. I have learned something new today, thank you for that.

RIO systems maybe obsolete by today's standards, but it does not mean that RIO is not still prevalent out there. I currently have a customer who continues to spec the SLC 5/04 CPU as they do not want to migrate from their existing DH+ network, so we are still installing RIO systems, which means block transfers for us. I recommend learning block transfers now when you have something you can play with, as it can only make you better, plus RIO can be used to communicate with other smart devices as well, which means block transfers.

You are correct in that you CAN use the discrete transfer with your setup. Perhaps the local tech guy didn't see the exact layout and details as you provided them to us. As a result of not seeing the full picture maybe that explains why they gave you the response that they did.

That aside, even though what you are doing is valid, I would probably recommend against it simply due to the future expansion issue. You really have locked yourself into these two-channel analog combo modules. If in the future you want a 4 or 8 channel card you might have to leave several consecutive slots empty to accomodate the memory requirements.

If later you decide you want to switch to higher density modules and decide to start using Block Transfer then you would have to readdress all existing remote analogs to their new locations.

So if this system will never expand, then go for it, otherwise, I would suggest you make use of Block Transfers. With the 5/05 processor that you have the BTR and BTW instructions are pretty straightforward.

OG

I personally would always do it with block transfers
as you need to write and read to that module.

Another reason is just because you can why would you, do it differently to how most would expect it.
you or someone else some day will try understanding why its done like this