Powerflex DNet Help

Hi all.....thank you for looking

I'm working on a project with 2 Powerflex 700 VFD drives with 20-COMM-D DNet adapters.

The 20-COMM-D has the ability to use the "Get_attributes_Scattered" (Service ID = 4B)

I am trying to use the new DEM instruction but I'm having problems trying to find where to place the parameter numbers I want in the "Send Data"

Can some please comment on this?
Thanks

This sounds like a Ken Roach question. Maybe we can get the master of Devicenet to help on this.

I'll take any help I can get.
I did see another post regarding the Scattered DPI Parameter Object, but there are no "examples".

The 20-COMM-D manual (Starting on page C-22) gives instructions for using this object, but it contains data fields within an address block (in this case N30) for:
- TXID
- Command
- Port
- Service
etc.

View attachment PowerFlex 20-COMM-D Get_Attribute_Scattered.pdf

Then it goes on to list starting at word 7 to populate this address with one of the parameter numbers you are requesting....then 2 pad words.....then next parameter etc. Up to 8 parameters.

Now this is all fine, but the DEM instruction takes care of all the DNet attribute data and I'm ASSUMING that the parameter request values will go in the "send data" block.....but really guessing and testing could take forever with pad words in between as I'm unsure if a value in the pad word would cause an error....

So again.....ANY help....I really just need to know where to put the value for the 8 parameters I'm requesting, and it would be nice to know where they come back. The Control block for DEM has to be 70 words, so I'm guessing all data will be containing within.

Thank you again

Your guesses are right on target; the request block for a DEM instruction to execute the Scattered Parameter Read is arranged as follows:

Parameter Number
Pad Word 1
Pad Word 2
Parameter Number
Pad Word 1
Pad Word 2
....

The response includes the Parameter Numbers in the corresponding words, an the 16-bit or 32- bit parameters values in place of the pad words. If the parameter is a Floating Point data type, you need to COP the Pad Words into a single Fx:y element.

I did a project two years ago that used this extensively; I'll go see if the code is still in my archives. I do remember that I needed version 6.x or better of the 1747-SDN because 4.015 (very popular and widespread) didn't execute Scattered Reads correctly (though it did Get/Set Single correctly).

Thanks Ken!

So If I understand this correct.....the DEM instruction uses a Control/Data Block. The Service code, class, instance etc. is set up under the general tab.....and does not have to be set up in the control block?

The SLC instruction help for the DEM instruction defines the control block as: "It is a block of words containing the status bits and other data associated with the instruction. It also contains the send and receive data."

But it does not map the status bits within the control block.....only within the general tab.

If I were to use N7:0 (the block has to be 70 words). Then If I wanted paramenters 1, 15, 254, 72.

I would then assign the DEM to the correct Send data size in this case 20 bytes and then populate the block as follows:

N7:0 = 1
N7:1 = 0
N7:2 = 0
N7:3 = 15
N7:4 = 0
N7:5 = 0
N7:6 = 254
N7:7 = 0
N7:8 = 0
N7:9 = 72

I've Used the information from the manual (and also the attached pdf above) to configure the general tab acording to this screenshot:



Any comments you will are truly appreciated!

I found my old program from July 2008 and extracted the DEM logic.

The DPI Scattered Parameter Read can be a tricky function. My logic brought back a couple of tricks, like the parameter numbers having to be in the high byte of the outgoing word, and the write block being 49 bytes instead of just 48 (8 parameters x 3 words x 2 bytes per word).

This example program might help you. I'm going to check to see if this is written up in the Knowledgebase or Sample Code website.

Make sure you have at least version 8.005 firmware for the 1747-SDN; there were some bugs in the early 8.x that had the potential to scramble data.

Page 12-57 of the SLC-500 Instruction Set Reference includes a map of the DEM control block that shows the message payload begins at Word 12 for Send Data and at Word 41 for Receive Data.