SLC 5/05 Remote I/O Addressing Sanity Check

[robertmee]

Had a Customer send me a large design with all the I/O mapped out, and it is something different than what I normally do, not to say that it is not correct. So, in that I'm almost exclusively CLX nowadays, I'm a bit rusty. As an example, the first rack is hanging off of slot 1 SN module with a 1747-ASB. It is an 8 slot rack. Slot 1 is an 1A16, Slot 2 is an OW16. They have denoted to use 2 slot addressing (which doesn't seem logical for 16pt cards) and they have indicated that the IA16 module is I:1.0 and the OW16 is O:1.0. I've always used single slot addressing such that IA would be I:1.0 and OW would be O:1.1. If it makes a difference the rest of the ASB is 10 Powerflex 70's in 1/4 rack configuration (starting at Rack 0 Group 4).

So, my question, is A) is this even possible and B) what's the advantage?

EDIT: Doing some further reading I'm really getting confused on this. I understand that 2-slot addressing uses two slots into one 16-bit word of the Input and Output Image table. So, maybe alternating Input and Output modules fills up a full word of each Image, saving a word. However, page 3-3 of the ASB module says that 2-slot puts slot 1 in the low order byte and slot 2 in high order byte of each image word. So that doesn't seem to support it working. I would get only 8 of the 16 points in each image (the lower 8 in the Input and upper 8 in the output). Thoughts?

 

[CeCo3]

robertmee,

We have a 1747-SN with a FlexIO rack hanging on the other end (1794-ASB). I found the addressing to be confusing as well. I do not have time to explain it, so I've attached a spreadsheet that shows which modules are installed and the corresponding addresses used in the 5/05 program. Integer addresses correspond to analog I/O and the necessary block transfers.

I'm not familiar with the 1747-ASB, but the 1794-ASB has multiple addressing schemes.

I hope this helps.

CeCo3

 

[robertmee]

There's no attachment, but thanks for the response. I actually was at one time when slc's were all the rage pretty proficient, but in my own designs, I always kept the I/O addressing to single slot w/ 16pt modules as it lent itself to straightforward addressing. I don't have problems with G files or M files with Block Xfers, but this alternating Inputs/Outputs with 2 slot addressing to save a word is not something I would have done. I talked with the customer who laid this out and discovered everything was done to eliminate Block Xfers altogether. There are no analog modules in any remote racks and any Powerflex 70 drives that need additional data have been expanded to 1/2 slot racks instead of the traditional 1/4 (I have to verifty THAT will work too).

 

[kamenges]

The way I have always thought of this is that the number of slots in the addressing mode defines how many physical slots are tied to a single I/O image table word.

For example, 2-slot addressing will map a single I/O image table word (161 bits) across two physical slots (the slots MUST BE an even-odd pair, ie 0 and 1 or 4 and 5, but not 3 and 4). You can put a 16-point module in a slot but it will use up the whole I/O word, preventing you from puting any input module in the next slot. So you need to alternate 16-point modules. However, you don't need to alternate 8-point modules. And you can't use 32-point modules at all.

1-slot addressing will map a single I/O image table word to a single physical slot. Similarly 1/2-slot addressing maps two input image table words to a single physical slot.
Keith

 

[robertmee]

apparently that's what they are doing since they are alternating Input and Output Modules. Just seems counter intuitive as you are restricted to using pairs. It also doesn't seem to jive with the ASB manual as it says this:

2 Slot Addressing
Input Image
0-7 = Slot 1
8-15 = Slot 2
Output Image
0-7 = Slot 1
8-15 = Slot 2

So, that would seem to indicate that the Input image would only get bits 0-7 from the Input Module and that the Output Image would only get 8-15 of the Output module. Almost as if you had an 8bit input and output module in each of those slots.

 

[kamenges]

If you had only 8-bit modules you wouldn't need to alternate. The reason they state this the way they did is it definitively tells you which module gets which bits if you are using 8-bit modules. If you are using 16-bit modules then the single module would stil get all 16 bits. There just wouldn't be any bits left for any additional modules of the same type.

Also keep in mind that both the input and output image tables get a 16-bit word across both slots. This is why you can have a 16-bit input and a 16-bit output in each of the 2-slot pairs. Also, 16-bit modules with 2-slot addressing is also the most efficient from a word utilization standpoint. You don't have any wasted words.

Keith

 

[robertmee]

Thanks again for the explanation. I see the benefit of condensing words in the case of a full SN module. Not that they are doing it, but for my own education, what happens in this scenario if someone wants to drop an analog module into an empty slot. Does 2 slot addressing support analog?

 

[kamenges]

Originally posted by robertmee:

Does 2 slot addressing support analog?

You just had to throw that one at me, didn't you? And I was doing OK up until then.

I've never used analog modules with anything but single slot addressing so I don't know how they would show up. I'm sure someone will come along and let us know.

Keith