Typo in 1756-rm001?

Cf. here.

The Logix manual says the CTD instruction behaves like this:But I think, and the flow charts on the subsequent pages imply, it might actually behave like this:Could someone with actual knowledge and/or hardware please confirm which it is? My MicroLogix does the latter, AFAICT, but assuming the 500 and 5000 instructions are identical seems less than wise.
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L75 controller V31 works as shown on second diagram - tested

Edit: Also tested L85E in V34 - second diagram is correct, DN bit goes OFF after ACC<PRE

My understanding of things is that the latter is correct (ie DN is true when ACC >= PRE). Give me a few minutes and I'll test with 5000 to verify.

EDIT: It does indeed in a 5380 running v32.

In fact, given that CTU and CTD adjust the DN bit regardless of the rung-in condition, it would be somewhat absurd to do it the other way -- otherwise any program that used both a CTU and CTD with the same counter tag/data would constantly toggle the DN bit when the ACC was equal to PRE.

Thanks both of you.

Yes, I though it seemed absurd as well, but with Rockwell I thought it was better to ask.

Those manuals are pretty good, a gold standard that makes all others seem like Pb, but there are still the odd typos.

drbitboy said:

I though it seemed absurd as well, but with Rockwell I thought it was better to ask.

Click to expand...

True enough!