SLC500 Remote I/O questions

keithb

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Join Date
Aug 2002
Location
Basingstoke, UK
Posts
53
Hi

I hope that someone can help me with some info on SLC500 remote I/O.

I have a project that requires the following I/O modules installed in a 13 slot remote chassis (1 slot addressing) connected to a 1747-SN RIO scanner in the local chassis. The CPU will be a 505

Slot 0 – 1747-ASB Remote I/O Adaptor
Slot 1 – 1746-IB16 Digital Input Module
Slot 2 – 1746-IB16 Digital Input Module
Slot 3 – 1746-IB16 Digital Input Module
Slot 4 – 1746-OB16 Digital Output Module
Slot 5 – 1746-NI8 Analogue Input Module
Slot 6 – 1746-NI8 Analogue Input Module
Slot 7 – 1746-NI8 Analogue Input Module
Slot 8 – 1746-NI8 Analogue Input Module
Slot 9 – 1746-N08I Analogue Output Module
Slot 10 – 1746-N08I Analogue Output Module

From reading the SN and ASB manuals it seems possible to do with block transfers, but I’m not entirely sure how to do it.

Correct me if I’m wrong, but I figure that logical rack 0 is a full rack (physical slots 1 to 8) and logical rack 1 is a quarter rack (physical slots 9 & 10).

Is it possible to configure the RIO this way? Can I get this much data over RIO?

Just to throw a spanner in the works, there will be another scanner in the local chassis connected to a similar RIO setup. Is this possible?

Some background: The client is driving the hardware selection … I wouldn’t have done it this way, but we have little choice. I would have gone for CLX and Profibus or DeviceNet/ControlNet.
 
kethb said:
From reading the SN and ASB manuals it seems possible to do with block transfers, but I’m not entirely sure how to do it.
The 16-channel digital i/o will be accessible in the userprogram via direct input and output adresses.
The 8-channel analog i/o will have to be accessed via block transfers. I believe there are block transfer application examples for each analog module type on ABs knowledgebase.

keithb said:
Correct me if I’m wrong, but I figure that logical rack 0 is a full rack (physical slots 1 to 8) and logical rack 1 is a quarter rack (physical slots 9 & 10).
Is it possible to configure the RIO this way? Can I get this much data over RIO?
Yes + yes.

kethb said:
Just to throw a spanner in the works, there will be another scanner in the local chassis connected to a similar RIO setup. Is this possible?
Yes.
 
You have the basics laid out correctly. If there are no surprises like a main chassis full of complex modules, then this will work fine.

You will want to use "1-slot addressing" mode on the chassis controlled by the 1747-ASB. The 1747-ASB will be addressed (as you described) as Logical Rack 00, and because you have more than 8 slots, the Slot 9 & 10 locations will be considered the first 1/4 Rack segment of Logical Rack 01.

You really don't even need another 1747-SN scanner in the local chassis to scan another 13-slot Remote rack; you could daisy-chain the RIO wire and scan another chassis of this size. The block transfer speed would necessarily be slower.

Using Block Transfers in the SLC family is easier than it used to be because of the addition of BTW/BTR instructions to the SLC instruction set a few years ago. It still requires a little familiarization with the arcanum of A-B's "Rack/Group/Slot" addressing method, which is simplified by using the straightforward "1-Slot Addressing" method.
 
sorry I don't have time to dig deeper right now ... but here's one "Common Problem" tip that might help ... the 1747-ASB will NOT be located in "Slot 0" as you showed it above ... secret handshake: using the ASB shifts the chassis addressing around - and the ASB doesn't have a "Slot Number" assigned at all ... specifically, your first 1746-IB16 will be located in "Slot 0" - and then so on down the line ... people who miss this fact usually get their Block Transfer addresses "off-by-one" slot ...
 
1747-SN RIO scanners in the chassis with the SLC controller appear to the SLC like I/O modules with large data tables (up to 32 words Input and Output data). The general address format is I:slot.word/bit and O:slot.word/bit.

With the 1747-ASB set up to begin addressing as Rack 00 and using 1-Slot Addressing, the I/O modules in the remote chassis would be addressed as (where s = Slot number of the 1747-SN):

I:s.0 1746-IB16 Digital Input Module
I:s.1 1746-IB16 Digital Input Module
I:s.2 1746-IB16 Digital Input Module
I:s.3 1746-OB16 Digital Output Module
BTR to R00/G04/S00 1746-NI8 Analogue Input Module
BTR to R00/G05/S00 1746-NI8 Analogue Input Module
BTR to R00/G06/S00 1746-NI8 Analogue Input Module
BTR to R00/G07/S00 1746-NI8 Analogue Input Module
BTW to R01/G00/S00 1746-N08I Analogue Output Module
BTW to R01/G01/S00 1746-N08I Analogue Output Module

You choose the Integer file registers that are used by the Block Transfer Read (BTR) and Block Transfer Write (BTW) instructions to the analog modules.
 
Above, I've oversimplified a little bit, because the 1746-NI8 modules require both a Block Transfer Read (to get the Input data) and a Block Transfer Write (to send Configuration data).

Examples can be found in the RA Knowledgebase:

Answer ID # 17814 Block Transfer for 1746-NI8

Answer ID # 18461 Omnibus BTR/BTW Examples Act of 2007

and in the Literature Library:

Publication 1747-UM026, 8-point Analog Output Modules User Manual


During this project you'll probably find yourself wishing the analog modules were in the local chassis just for ease of use, but it's completely possible and practical to put them in a Remote chassis using the 1747-SN/ASB RIO link.
 
Ken Roach said:
You really don't even need another 1747-SN scanner in the local chassis to scan another 13-slot Remote rack; you could daisy-chain the RIO wire and scan another chassis of this size. The block transfer speed would necessarily be slower.
Good point ! I dont know the exact RIO data transfer rate but a quick calculation of how fast the maximum of 32 input words and 32 output words plus overhead can be transmitted @ 57.6k gives approx 30 ms. If this is acceptable for keithb, then there is no reason to spend two SN scanners.
 
Thanks for all your replies and the links. I'm starting to understand it a bit better now.

I've done a fair bit of PLC5 stuff, so I understand the rack/group/slot thing. Just got to get my head round it again as it's a long time since I've touched a PLC5.

Ron, thanks for the "secret handshake". It's stired my memory from when I did some SLC remote I/O (discrete only) a few years ago. So, assuming the scanner is in slot 1 of the local chassis, the first remote input in physical slot 1 would be I:1.0/0. Is that right?
 

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