PLC 5/40 BTR and BTW instruction help

de_arnab

Member
Join Date
Jul 2006
Location
Louisiana
Posts
24
Hello,

I'm new here and looking for some help from you all. I'm writing BTR and BTW instructions in RSLogix 500 for a 1794-IE8 card with 1794-ASB adapter (remote IO) and have some questions on each of these intructions.

On the BTR instruction my length is 9 as it got 8 AI channels and the 9th word is the status word. Do I make it continuous or not ? For the control block, I guess I don't have to set up any values for the 5 words that it uses.

On the BTW instruction, do I put the value -256(decimal for 4-20mA) on the write word 0 of the data file? And, how do I choose the length for this instruction? It's a 8-AI card and the user manual don't say how to choose the length specifically. Also, whether it will be continuous or not ?

I read a lot of knowledgebase tech notes from ab.com but they didn't clarify this with a 5/40 controller using 1794-ASB modules. Maybe I missed it. Any kind of help will be appreciated as I'm doing it for the very first time.

Thanks in advance to all of you.
Arnab
 
Here's a code snippet from a 1771-IFE, should be similar, notice that the write is only preformed when needed. There is also a good read status bit.


blockxfer.png
 

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