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Old October 1st, 2003, 03:12 PM   #1
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Power Flex 70 Drives on Device Net

I am currently working on a project using the Allen-Bradley Power Flex 70 drives and configuring them on Device Net. Also we are using PLC 5/40 E. When you configure a drive on D-Net, D-Net writes 2 words of memory per drive to the scanner module. In our ladder logic, we have to use BTR & BTW logic to configure these words. The max length of words in the BTR & BTW is 64. Well in our job, we are looking at configuring 42 drives! This means a total of 84 words of memory. How do I configure this many words of memory in my PLC. Can I use two sets of BTR & BTW to write the 84 words to the scanner module?
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Old October 1st, 2003, 11:02 PM   #2
Eddie Willers
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The 1771-SDN can actually accomodate several BTR/BTW sets to access a total of 357 words of DeviceNet Input and Output data.

If the PLC-5 is sending several block transfers to the same slot, the module can only tell them apart by size.

62 Words - BT #1
61 Words - BT #2
60 Words - BT #3
59 Words - BT #4
58 Words - BT #5
57 Words - BT #6

That's 357 words of Input, and 357 words of Output. That big old piecewise data table can be shared by both channels of the 1771-SDN.

Making a scanlist for both channels is kind of a clunky process; read the RSNetworx notes on that carefully.

The Installation Instructions for the 1771-SDN are the best reading on the matter. They're on
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Old October 2nd, 2003, 01:16 PM   #3

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Hi, yes you've gonna make two btr ab btw. First one in word #62 in the scanner and the second in word #61.
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Old October 2nd, 2003, 07:02 PM   #4
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Let me jump in here an warn you about a MAJOR problem with RSLogix 5 and the DeviceNet scanner.

DO NOT configure the 1771-SDN in the configuration wizard!! This will cause problems with the multiple BTR/BTWs' that you must perform to the module to get access to the total available 357 words that Eddie mentions. I worked with someone who did this in order to get access to the devicenet status data and it caused an automated crane to drop drop a charge bucket for an automated cupola charging system. Of course once the cupola is running you don't want to stop it so you can imagine how tense things (& the mechanics got the crane back in working order) were while he reloaded the old program. It took me a day to figure out that the chassis configuration was causing the issue. Of course Rockwell just says that they never use the configuration wizard anyway.

Just be careful. I can create an example file that will show the problem and it is visible in the offline file.


Last edited by dash; October 2nd, 2003 at 07:05 PM.
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